I would love to see some sort of archiving features in vBulletin. But just archive everything over x days old isn't exactly what I would like to see. Running a technical based forum, the same questions come up over and over again, so here's my idea for how to archive them.
Basically you would have a forum, and a corresponding archive for that forum. Then if a thread reaches a set rating with a minimum number of votes, the thread is automatically moved to a non-writable archive for that forum. That way only the good threads are archived, and you can then prune the forum without losing anything good.
Options for it could be:
Moderator approval - have an admin page where the threads are stored in queue. If the moderator ok's the move to the archive, then the thread is moved.
Choices of where to move - give users the choice of moving threads from one or many forums into one or many archives.
Archiving variables - allow the rating and minimum number of votes to be set in the control panel, or another admin page.
And something else that might be an entirely different hack would be download archive. Something to basically turn the entire archive into one big HTML or zip file that you download for your own use at home.