Hi Pete,
I think the easiest way of falling into threads that contain a high percentage of sensible, decent conversation is to choose the ones whose title looks like it's about something specific.

It seems to me that anything with 'folk' in the title seems to degenerate into a bit of pushy-pully. Good information sometimes, but more insults.

I guess you've probably found the search feature? You can use that to dig up old threads on nearly anything you can think of. If you reply to those old threads, they pop onto the current list and sometimes revive into neat discussions as people add stuff they've found since the last time the thread was current.

Also, there's a good 'newcomers guide' thing which is a clicky at the top of the threads on the list.