The fewer threads to search through to find information on a topic, the easier to read everything said.

I think older threads often have more good informed contributions than newer ones. At worst, I've, on more than one occasion seen opening replies in new threads start off with myths that have been debunked in the past and someone ends up having to come in to sst the record straight for the nth time.

Reopening an old thread does not prevent any past contributer (if still around) from revising thier thoughts. In fact to see thread with the text there should make it easier. One thread should also make any changes of idea clearer than having different ideas posted in several.