I also moderate on a site that uses vbulletin.
phpWebsite Support Forums
http://phpwsforums.comIt is strictly a forum site and was originally run with phpBB. Due to hackers and spammers, phpBB was dropped for vBulletin. Setting new members to moderated has drasticlly cut down on the spamming and the users see nothing.
Since the current forum topics can be imported into vBulletin, I'd say that is the way to go. Even better if the rest of what the current site offers can be built in around that over time.
I've looked a Drupal. I've seen some rather nice looking and functioning site, also alot of dreadful ones. I attribute that to Drupal being a CMS framework and not a CMS portal package like Xoops. Basically, a new site would have to be built up within the frame work before content could be added. Alot more work but less than coding all the php for a new site.
Have you checked out phpWebsite?
http://phpwebsite.appstate.eduGotta pug it, being a moderator for one of the support sites and all! :-D