I think that having a generic "thumbs up" symbol not attached to any reputation or specific text would be more widely useful in this case. Then when clicked on, for example, an Acronym Game post, it could be taken to mean "nice one etc.", for a Bargain Basement thread, "Thanks", or for a discussion, "I agree etc.".
As for the "thumbs down", I know it's a controversial one, but I think it has a place as long as it has no meaning outside of itself; it's purely a way for users to say "I disagree" or "Eeeeeeeew!" with no comeback on poster or clicker.