Valverde and Boonen's cycling universes were so different that they rarely overlapped, even though they both turned pro in 2002. Valverde's natural territory is the hills, while Boonen's was the cobbles, although they did occasionally cross swords. The most memorable occasion was in 2005 when Boonen outsprinted the Spaniard for gold in the World Championships in Madrid. And after 15 years of pedalling along parallel career paths, one particular weekend this April proved significant for both of them.
For Boonen, the red-letter Sunday came when he pulled down the curtain on his career in the Roubaix velodrome, following a respectable but fairly unremarkable final Classics swansong, garnering one low-key win in the Vuelta a San Juan to maintain his record of at least a win a season since 2002.
Valverde's red-letter Saturday came when, on the eve of Boonen's farewell race, he won the Vuelta al País Vasco for the first time in his career, bringing his victory count for 2017 to nine. "My best spring ever," was his own analysis at the time, and you'd be hard pushed to disagree. It's been extraordinary: he's won the Vuelta a Murcia, a stage and the GC of the Ruta del Sol, three stages and the GC at the Volta a Catalunya and a stage and the GC in the Basque Country. Following that, he won Flèche and Liège.
From here on, comparisons are futile, given that Boonen has retired while Valverde has said that he'll forge on, at least until the end of 2019. All of which raises an apparently simple but actually very complicated question about the Spaniard: what is there left for Valverde to aim at in cycling, when, like Boonen, he's won pretty much everything he can, mostly several times?
The more cynical would point out that Valverde is being paid a lot of money to race until 2019, so of course he'd want to continue. The purists would argue that as long as the Movistar rider is enjoying winning streaks as golden as this spring's it would be nothing short of ridiculous to consider retirement.
You could also argue that we're thinking about it a lot more than Valverde himself, who is sanguine about the whole thing.
"If I had to retire tomorrow because of illness or injury, or for whatever reason, I wouldn't be at all unhappy or bitter; there wouldn't be a sense of something missing," Valverde tells Procycling one rainy spring evening in Catalunya this March. "It's that lack of pressure that helps me succeed now. I've practically won everything I can at least once. Don't get me wrong, I like to win – both for myself and for the team. But I'm feeling so relaxed now, it's almost as if I'm racing better as a consequence."
For years, the elephant in the room for Valverde was his two-year doping sanction from Operación Puerto. And as the seasons have rolled past since his return in 2012, Valverde has ridden as well as, or better, after his suspension than before. Doubts about his past no longer seem to shake Valverde. In 2012 and 2013 questions about his ban brought strained, truculent answers. Now, he's more forward. After he won Liège-Bastogne-Liège for the third time, in 2015, one Belgian journalist asked him to explain - nudge, nudge, wink, wink - how it was possible he could triumph in such a difficult Classic nine years after his first victory and with a doping suspension in between. Valverde answered simply and without the slightest trace of anger in his voice: "Because I'm damn good."
In the last couple of years, Valverde has stopped being the restless bag of nerves he used to be, on and off the bike. When you remember the countless times Valverde used to freeze in the headlights when he was on the point of racking up another success, that matters.
Valverde used to fluff his lines a lot when everything was in his favour. There was the time he lost the 2006 Vuelta a España at Sierra Nevada, by closing down one downhill attack by eventual winner Alexandre Vinokourov, but then failing to react quickly enough when the Kazakh bolted away one last time. Or when he lost all chance of winning the 2008 Vuelta in a panic-stricken solo chase after going back to the team car for his rain jacket rather than sending a team-mate to get it. His two silver and four bronze medals at the World Championships are an impressive, record-setting result. But it's also kind of impressive how Valverde's managed to get hitting the goalposts but not scoring down to such a fine art.
Either way, at 37 Valverde is making up for lost time. His win at Catalunya was his first at a WorldTour stage race since the 2009 Vuelta, which he won before his ban.
Catalunya confirmed how laid back Valverde has become. The evening we talked was the same day he'd been awarded the leader's jersey after a team-mate, José Joaquín Rojas, was penalised for pushing in the team time trial. The media was fizzing with a story that left Valverde at the centre of a controversy and, indeed, we'd felt it wise to check beforehand with Movistar that the interview would go ahead. But the green light came through and Valverde was so untroubled that he extended it, just so he could talk about what would have been his choice of alternative career.
"I'd have been a lorry driver," he says with a grin, "just like my father was." Then he segues into a discussion of why lorries appeal: "It's nothing to do with the travel or seeing the world, I just like them." He talked at length about which type of lorries he can drive and there was no sense he was under pressure from the media storm.
The next day, after an early morning change of opinion saw the UCI commissaires decide to penalise all of Movistar's riders by a minute, stripping Valverde of the race lead, he didn't throw a tantrum like one of his directors and threaten not to race. Instead, he outclassed the uphill sprinters on the ascent to La Molina (the same climb where he lost the race to Richie Porte in 2015) before retaking the leader's jersey with a devastating climbing display at Lo Port on stage 5. For good measure, he rounded the Volta off with a superbly calculated sprint from a small group to take the final day victory in Barcelona's Montjuïc Park. The old Valverde might have lost his head under the sort of stress he'd had to contend with during the past week: Catalunya showed us that the new one seems either to thrive on it or simply doesn't notice it.
There have also been other changes, Valverde says, such as noticing that the years are ticking by, albeit only when he's not racing. "It's harder and harder to start travelling again in January. Once you start, though, it's not such a big issue because you're on the road.
"That's why having a stable team life, like I've got with Movistar, matters. And also why getting away from it all on holiday with my wife is very important, even if last year we could only do that between one Grand Tour and the next, and there was hardly any time."
Even though he's clearly a racing addict, Valverde now has to face a new UCI-imposed maximum limit of 85 racing days. "It's not a bad thing – it's higher than most riders get to anyway, which is about 65 or 70." It goes without saying that Valverde is on the limit himself: "82 or so this year."
So rather than asking why Valverde wants to continue, perhaps we should be asking what it would take for him to stop. If, for example, he managed to win Amstel Gold, Il Lombardia and the World Championships – the three most glaring absences from his palmares – would he quit straightaway in order to go out in a blaze of glory?
"No. I can't imagine retiring like that when you know you can win more," Valverde replies. "I'm not obsessed with winning the Worlds. I've still got a good chance of winning it. Taking so many medals shows that."
He bristles, slightly, when it's put to him that – six medals or not – for now Óscar Freire remains Spain's best racer at the Worlds. "Óscar was always more of a Classics specialist than me," he counters, "but I've won a lot that he hasn't."
Given that both have won Monuments – Freire Milan-San Remo, Valverde Liège – the trump card would, of course, be the Vuelta a España. This was last won by Valverde in 2009 and will, after the Ardennes (where he won a fifth La Flèche-Wallonne and a fourth Liège-Bastogne-Liège), be Valverde's main goal for 2017. He'll be Movistar's sole leader in Spain, given that the defending champion, team-mate Nairo Quintana, won't be there. Valverde says, "The initial aim is the podium." But he believes a second victory could be within his grasp.
"It's a good route for me this year, very hard, and I love the fact that it goes through my home region [of Murcia]," he points out. "But, really, wherever I go this year, it's an objective. It's only in the Tour where I'll be working for Nairo, 100 per cent. I was a leader in the Ruta del Sol, here again in Catalunya, again in País Vasco and so on and so on. None of them are absolutely vital goals, but everything's a goal."
Valverde recognises he has to have some limits, however, so he won't ride all three of this year's Grand Tours, as he did in 2016. "I'll be able to say I've done it, when I retire, but I don't want to do it again."
Nor does he mention winning the WorldTour individual rankings, something he's done no fewer than four times in the past, as a possible goal. And there's little other unfinished business. "I'd like to do Flanders, if only to say I've done that."
Valverde continues: "I'm going to be honest. I could say I go on racing because I've always dreamed of doing it. But there are a lot of bike racers who would say the same. Really, I go on racing because I'm good at it, because I've got a talent for it. I am naturally competitive. When I'm training in a group, I'll find I've started racing with the rest of the guys to be first to the traffic light or village boundary sign, that sort of thing.
"Sometimes, my competitiveness gets too much. But ultimately, and here's another reason for continuing, I feel like I'm lucky, privileged, because my racing life means that when I'm at home with family, I'm really there, really 'at home'. Some riders like to train until the early evening, but I'll be up early and do my training before lunchtime, so I know that I'm always going to be able to spend all of my afternoons with my family.
"It'd be far harder for me to do that and spend so much time with them if I had one of those standard job routines, working" – as office-bound Spaniards do – "from nine to two and then four to half past seven."
That might explain why he continues at 37, but as for winning so much? Once again, Valverde comes back to his being relaxed as acting as a catalyst for success. "If I don't worry that I have to win, that naturally good condition comes through on its own."
It's easy to see, too, that Valverde's emotional involvement with his sport remains just as intense as it was in 2002. A quick glance at Valverde's roars of delight at the end of the Eibar time trial in País Vasco and his hugs with a Movistar soigneur reveals how badly he still wanted that long-awaited victory.
Valverde claims that he would leave the sport with no regrets if he had to quit tomorrow, but looking at the sheer joy with which he celebrated that first País Vasco win in 15 years, you get the feeling he might well be kidding himself. And that, ultimately, is why he's continuing to race, while Boonen – equally happily, let's not forget – will be watching next year's Paris-Roubaix on television.