I'd actually prefer for someone to start a new thread on the whatever it is is they want to re-discuss, and if necessary, link to the old thread for reference. Usually no one will remember threads from even 6 months back, and even if they do, I think it's okay to talk about something which has already been talked about, as situations change and new people are now here. Plus if an old thread is bought up, someone might avoid responding to it, as they realize by viewing it that they already had their say there. But on the other hand, if a new thread is started on the subject, the person may be more inclined to talk about the subject again.
Although sometimes there are times when bringing up an old thread is more appropriate ... such as the Picture thread which is very old. However, it's difficult to determine which is appropriate and which is not.
On deleting, I'm very against that, as I don't like to see OWF history deleted. And I like keeping stuff.
Abe Babe...