The topic of what makes a 'real' champion is an interesting one, and I'm not sure if I fully agree with anything that's been expressed so far. To me, riders that I respect will go for the win, but also go for whatever they can get if they can't win. Gilbert being too good for the sprint for minor placings to me is as insulting as Valverde (or Gerrans) not caring enough about the win to chase.
Situationally, I appreciate when riders will work together for the win, even if one of them is dragging a 'better' sprinter. Sometimes it will turn out like Het Volk this year and the Stannards will beat the Van Avermaets unexpectedly. I remember one year when Boonen did this in chasing Cancellara, just pulled and pulled and no one else would cooperate. He complained in the press afterwards, and he lost, but kudos. He didn't sit up, he spent his energy trying to pull back and then got 5th or something. Or the year the Schlecks went to the finish with Gilbert of LBL - they must have known there was a 99% chance he'd torch 'em in the finale, but they still went for it. Much as I am loath to heap credit upon Schleckdom, credit where credit is due in that instance.
So yeah, Valverde rarely shows that kind of initiative on the highest level. Someone who has the opposite reputation like Contador sometimes does the same (take the Dauphine where he gave it away to Talansky because he was marking Froome until it was past clear that Froome wasn't a threat), but he does enough attacking in races when there is less on the line (T-A for example), or relentless all-in attacking when he is on the back foot (2011 and 2013 Tours, 2012 Vuelta) that it more than makes up for some caution before the outcome is settled. I mean, in 2011 he made that downhill attack in the rain that made the Schlecks lose time and forced Andy's hand on that epic attack... if a rider is attack-minded enough to put Andy freakin' Schleck in the mood for an epic ride, that is to be praised (on the other hand, when the outcome is up in the air and he's not on the back foot, you get friggin' track stands on the Tourmalet). But that is one reason I like Contador's riding style - he could have kept the podium on at least the 2013 Tour, but finished off it in both the 2011 and 2013 Tours (well I guess technically he was DSQ from 2011 but whatever) because he cared only about the win, but even when he was caught he did the best he could. Dan Martin is a rider that has those qualities too, some opportunistic attacks in late times got him his 2 monuments, competing for minor placings has gotten him respectable results in others, but that long range attack in Catalunya gives him some cache as well.
I suppose that's easier to do in a stage race so I shouldn't complain too hard about Gilbert not sprinting it out in a one-day race, but it still seems disrespectful to the race, and the actions of a sore loser to take your ball and go home when it becomes clear that you won't win, you know?
Anyway, all that said, I am generally fine with Valverde torching the field with long attacks in smaller races (what was it, Roma Maxima and Andalucia this year?) but going with a different tactic in bigger races where he can't shed the field that easily. That makes sense. And I have a certain respect for the fact that he seems cool under pressure to the point of not caring if he gives away the win, if others aren't going to cooperate. That's a cool bluff if it works. But it rarely does, and the head-shakingly infuriating ease with which he gives up the chase when someone attacks makes him the most disappointing rider of this generation, while also being the most consistently excellent. Seriously, someone should make a GIF of that Lombardia finale - he half stands, pedals a high cadence for like THREE pedal strokes, and then sits down and looks around before he's even begun to accelerate after Martin. His 'chase' of Costa in the Worlds last year seems like a marathon by comparison.
tl;dr version - I don't think that not trying for minor placings is the mark of a rider I respect, really. I appreciate trying to win, and I appreciate that there is a certain honour in trying for the best result even if you don't win. Valverde does suck, but the qualifier is that he only sucks most of the time. Took a few words to get to that point.