I think this brings us right back to my opinion that the only way to successfully mediate the agree/disagree problem is to use a slashdot style system where the voter is forced to chose among preset descriptions, such as 'informative', 'insightful', and the like. It sets up a psychological barrier to just saying 'I agree', or rather 'this person agrees with me' which is really what they're saying. The other thing worth doing is to take away the incentive to reward or punish members through voting by having the votes only affect the post itself. Of course, no system will prevent the +1 vote 100%, but then it probably doesn't need to.
I do think there are benefits to the "thanks" system over the +1/-1. It's a nicely done mod - far better than what's been adopted here. It might help increase voting if nothing else, since the user rating includes votes given as well as received.
I think the real problem in switching to a slashdot style system is finding a mod that does it. The only one I can find has been abandoned, but then, that was only a cursory glance at what's out there.
My suggestion, if there isn't a way to do a slashdot-style system, is to try the 'thanks' mod and if that doesn't solve the problem, then toss the idea in the bin. I find it hard to believe that anyone honestly thinks that swapping icons will make any difference whatsoever.