Presumably, if a new thread started automatically, there would be links between them, so it wouldn't be too bad.

Personally, I enjoy the lengthy parentheses that seem to occur - even when they stop being parenthesis and become a totally different subject. It is so exactly like conversation - especially after a few glasses of Chilean Shiraz.
Does it really matter if we stray off topic? and rehash old topics? Rehashed topics don't always cover the same ground, and will quite often lead on to fresh fields, etc., etc.. ( Look at that!! five punctuation marks for six letters that aren't initials!)