I agree with thanks/rep not really being needed. Since I don't really see a point to it, on forums that I've seen it been used before, it never really ended up having a point. It either didn't work well like on HF (rep can only be given by paying users, rep isn't given on a per post basis, etc.), or it worked (wasn't typically exploited and was used how it was hoped) anyone could give thanks and so it typically ended up as posts that released things or tutorials received the most, then general helpful posts received some, and random posts wouldn't receive any. But at the end of the day even on forums where it appeared to work, I didn't really see a point to it as it didn't really do / change anything. As if the forum didn't have any rep or thanks it still would've been pretty much the same.
I guess the reasoning behind it (as far as a community based one, not the actual business of managing the forum) is to encourage people to be more helpful/post more that is beneficial to the community (but really you would hope people would want to do that anyway, rather than having a community that is purely based around rep), and if the forum is large then if someone is helpful in one section and moves to another, the users in this new section can easily see whether the user is trustworthy (but this can easily be abused).
EDIT: Just remembered one forum that used a similar thanks system, also did it as a way to streamline the discussions more. So to keep the threads more discussion based, they made simply saying thanks be considered as spam, and so you would hit the thanks button instead. So that was one good point for it.