As there is a heavily enforced rule about not starting threads where there is a similar one, even if that similar one is 500 pages long, perhaps a post limit to threads might be appropriate? Say automatically close any thread once it reaches 200 posts or something? It might allow for a fresh feel to some topics which can run on for pages and pages, especially when people start some sort of bunfight over some imagined slight.
(There is also a rule about not reinvigorating old threads, which is kind of at odds with the previous rule.)
IMO topics on these boards need to be noob-friendly, and I think a good way to achieve this is to not have so many monolithic threads that people always get pointed to whenever a similar topic is started. I'm not saying endless numbers of open threads, just a post limit on one thread at a time. It might sound nonsensical to "split" long discussions over several threads, but really the total post count will be the same, just not in one huge thread that people won't read anyway.