Mark - while removing the profile feature will remove the possibility of a spammer delivering a payload (spam links) removing the profile registration won't affect the targeting of your site - that's because the bot just looks for sites to pump registrations through - I doubt very much that the bots check to see if they are successful or not.   The only true deterrent is a stronger captcha or blocking the default registration URL, or disabling registrations entirely.

I had changed my Register to Join in the Site Language and later changed it back to register. I was getting spam accounts there after. Going to switch back to Join, another choice word to use is Enroll however a simple way to keep the default registration page and the only work around I found for changing the name, however I wasnt doing it for spam before. Now that I do get a bunch of spam I am thinking of changing back to join. Register works for me but the captcha needs beefed up. This kills the email servers sender score making it harder to communicate with the real users.