I think the old thread rule is mostly to stop people from generating email spam from threads that predate the forums. Having said that, when someone else has already made a new thread on the topic, it might be best to link the old thread from the new thread.
I certainly agree with making sure that all the previous discussion is easily accessible from whichever thread we do decide to use. Search, in general, peaked in 1999 and has been progressively worse since. So anything that reduces the need to search for info is a good thing.