I post regularly on another, completely unrelated board with high traffic. There, what they call "zombie threads" -- old ones that have lain dormant for a couple of months or more, then brought back to life by someone with a new contribution -- are not allowed. The accepted etiquette there is to start a new thread with a link to the old one in the first posting, and to title the new thread specifically enough that the new contribution or question is clear.

Could that work here? Not the forbidding zombie threads part, but the encouraging new threads for new contributions on old topics part.