Ron, good luck with it. You're stuck between a rock and a hard place. If you down it the kiddies win again, and will feel they can bully the next guy. If you don't your network is crippled. It's a no win situation.
If any of the dos'ed to death rbls really want's to get back at the spammers it's easy. Write software that allows any ISP or business to use their mail servers and their customers/employees (via a foward to address) to maintain their own highly dynamic blacklist. Blacklists are just one kind of filter. If we could load software that allowed us to forward spams caught by other filters into it and it maintained a DNS blacklist we could have our servers use, we wouldn't need big public rbl's, everyone doing any kind of mail volume could easily run their own IF THE SOFTWARE WAS AVAILABLE. A distributed solution for a distributed problem. Resistance is NOT futile. Geo.