Hi David,
This is very common problem that we all are facing with the Buddypress websites. The combination of registration process that I am using to stop it
1. I have enabled social login as it is very easy for users to login with almost no spam users. Every users is having a google or facebook account. It increases the engagement of users also.
2. Restrict sign up with only a few legit and popular email domains like GMAIL, YAHOO, MSN aor anything u want. You can use BP Restrict Signup By Email Domain plugin.
