IMO it's NOT going to be updated at macworld. Maybe BY macworld, but the next imac revision is very likely just going to be some minor spec bumping, and that's not going to make it in to a keynote.
Also, maybe NOT by macworld. People have been counseling against buying minis for over 6 months now on the assumption that updates are coming soon. There's just no predicting with apple.
So all told, the answer is the same as it always is when someone asks this question - if you can wait, then you'll either get a better machine for the same price or the current machines at a nice discount. If you can't wait then the current models are more than adequate for basic uses.