unlike porsche club, you do not have to own a bmw to join. one great benefit is a discount at all hpde events held by local chapters.
also, you can participate in their annual raffle/fundraiser, which has a profit margin far less than most raffles.
if you have a bmw, one of their biggest advantages is that essentially all bmw technical questions are answered, in case you have a difficult diagnostic problem with your car, they often can be of help.
i haven't owned a bmw for 3 years, but i still maintain my membership.
for the bmwcca!