[noppid]

This is a common request and has been solved in many ways.

Try this, create a duplicate group of registered users called say full members. Create a promotion that after x days and or x posts, users get promoted from registered to full member.

Remove all the privileges for sigs and member profiles and avatars and such from registered users.

Keep doing what you do and add Stop the Registration Bots to your forum too perhaps.

Of course, as I said, others may have more suggestions.