Maybe a note on the "create new thread" page advising people to check up on the archives first might help...

I don't mean people should feel they should always revive an old thread rather than start a new one. Some of them get a bit long, and mayve there's a different angle that the new one is trying to open up - but it might be a good idea to stick a link to the precursor threads in the opening post.

For one thing it means we are less likely to have people leaping on us from a great height to tell us the previous threads existed, and questioning the rationale for the new one.