I have been using WangGuard for years and its the most effective registration spam busting plugin on the market. I always say that if you wish to kill comment spam you install Askimet but if you want to kill Registration spam you install WangGuard.

When I have a BuddyPress website with open registration I find it to prevent 100% of spam for my sites 100% of the time. Best of luck with the rebrand and I hope if you don't meet your goal the project can be picked up *cough auttomatic* *cough cough* so it can be integrated in future plugins *cough askimet* to prevent both registration and comment spam.