I always hated upgrading - I was a doofus and when I had my YaBB I hard coded things - such as using text links instead of graphic buttons because I was still on dialup and I wanted the board to be fast. All my coding would pop and I'd have to do it again. I finally installed a stock board at one point and I think I zorched previous posts.
I always looked for a thread based system that would just maintain 500 or 1000 threads and then self-zorch the oldest from there. My forums are dead - I used robots.txt to keep search engines out so that I could keep the membership to word of mouth. Except when Jason Scott showed up (from
textfiles.com) - a celebrity!
BTW - his video series on BBS's from back in the day, and it was really interesting.