first let me thank the spam fighters for doing a fine job.
I happen to know that as of YaBB 2.2.3 it is possible to require admin approval of new registrations.
I'm not saying this will cut down spam to 0, but it would keep those characters from getting in at all.
right now it's just register, wait for the forum's email, click and you're in. ready to spam in less than 5 minutes.
I know this would shift some work onto the main admins (doing the upgrade of course), but it's worth a shot.
as far as I've red, this confirmation mode also requires the aspirants to write a short statement as to why they want to get in.
surely a monologue about the amenities of V 1 A G R 4 or similar will not work here 