I would suggest creating a banned ISP listing with ranges based on persistent vandals, and when they suspend the accounts, you will unblock them at the firewall. It fixed my vandalism problems. I have 0% vandalism at the WikiGadugi site and I stuck it to WillyOnWheels.
Jeff
Jeff, you shoulda made this a board election issue - you could probably have gotten a ton of votes from all the good editors the vandals are slowly driving off.