The literally worst moderation move this forum has made is not deciding to auto-lock threads more than 5-6 months without reply. Even people who respond adequately to said old threads are edged towards making a new thread.
Old threads are sometimes relevant and might need posting in later. Also what Schneumer said is right, it's just some minor spam that isn't really annoying; it's not such a big deal that we need to lock every single thread.