Guarding Thread Resurrection?

This is kind of a judgement call, as if it's not done right the forums could get more cluttered (or less user friendly). Basically what I've been seeing lately is that new people come to the site and start reading through the archives, and inevitably reply to a post that's several months dead. Seeing that a new post has been made to the thread, more people continue to respond as if it were brand new. The black/red dots are a good start, but it seems people tend to still ignore the timestamp anyway, myself included. I guess it's just hard to notice if you don't remember the original thread.

Having threads close automatically after a set time might work, but then if more information is discovered, a new thread would have to be created to keep information up-to-date. What I suggest is having some sort of warning to someone who tries to reply to a thread that's over a couple months old.