Normally, if you actually contribute to a thread then by all means, if it's not giving the too old error.
But if you're just bumping it for the sake of bumping, or just adding some filler post that doesn't really need to be there, then I'm going to have to advise not doing that.
I don't think this guideline applies to files/S&R/clans/gallery though. I'm sure no one would mind if you bumped those on occasion, just, not excessively.