Craig, there's a vbulletin feature called "One Touch Ban & Clean" that you should be able to enable. I do lots of moderation on a very large forum elsewhere (I remember suggesting vBulletin to you way back in the day

) and we find that feature to be very useful, and make it available to the entire mod staff.
For preventing spammers from making it through, I believe vbulletin has features that stop auto-registration bots and such.