It is a catch-22. We need someone who is disinterested but not uninterested. We need a volunteer who doesn't want to edit there. We need someone who can practice spitting out little bits of gristle in a hobby or regional category, until they can bite off and regurgitate whole gallons of spam -- all without getting sick.
There is no solution, short of a death penalty for all spammers. What we use is experienced, trusted editors: and it's not as if we don't have something better for them to do, either.
One would be tempted to try a "spam fee:" charge $1000 for reviewing your site, 100% refunded if it's listed, 70% refunded if it's arguably not too far from being listable. The ODP can't do this (social contract and all), but Yahoo! is welcome to the idea (or any derivatives thereof.)