We have just changed from email registration to manual. A sysop will now have to filter each new registration request.
More work for us, and slower registrations for everyone new, but I agree, it's almost impossible to eliminate the spammers completely.
Thanks for taking these steps, even if it means more work for you.
Perhaps you can get some assistance from experienced forum posters (no, I'm not
volunteering ) if the workload becomes too much of a bother.