How about something real simple. E-mail verification. Have VB
send out the e-mail with a link to activate the account. Stay with the major players in e-mail like google or msn or even yahoo. Some applicants will have some sort of legit but odd address to verify. Small potato's in comparison to the trouble you're having now.
If you get an ass with a legit addy you can decode the e-mail header to get who it is and what ISP they're using.
Very little human intervention as VB
has it built in. The e-mail conformation that is.
As for the spam patrol you have to be careful who you put in the drivers seat. Some one gets pissed off and they could remove legit posts and threads as well.
Think this through carefully. You may just open up a bigger can of worms.