Upvotes/Downvotes for problems might be a good idea, but I can't see the point of comments.

Yeah, upvotes and downvotes on problems seem like a good idea, but realistically speaking, it just becomes another medium for spammers to simply downvote good problems. Trust me, a lot of people just go with the flow and keep on downvoting comments/blogs from lower ranked users even when what they contribute seems to be sensible or good. Also, a lot of crap gets upvoted too. People find downvoting fun, i guess? There have been various discussions in the past about this and needless to say will happen in the future too Don't know if it'd be the same for problems but one can most likely expect the misuse of such a feature, especially on CF with its spammers and fake accounts (which is very easy to create here and almost anywhere else). Shit happens when stuff like this is introduced, so it's better off the way it is. In the end, it's what most of the community wants and what sounds good to the Admins that will likely get introduced, which in this case is probably not happening.