In the Ardennes and often other perhaps less hilly races (such as stage 1 of the 2008 Tour), Valverde is very often a wheelsucker. Though one of his wins is from a group of 3, so he at least is smart enough to know which groups to be in, rather than just waiting for the bunch kick.
In stage races though, I don't really see how Valverde can be called a wheelsucker. Do we forget him helping to instigate an echelon attack in Paris-Nice? Going from way out on Mont Ventoux? Attacking to create a selection on stage 1 of País Vasco, thus eliminating Samuel Sánchez from contention? Sure, perhaps he wheelsucked through most of the key stages of his Vuelta win, but that's because he was winning. And he may have sucked Contador's wheel on Anglirú, but apart from J-Rod nobody else was capable of that, so it's an achievement in and of itself.
Valverde often makes races more fun. On the occasions where it's not because of what he himself does, but by forcing others to make it more entertaining because they have to do something because he'll beat you in the sprint.