I'm currently a member of RPA and have been for many years, but I agree it may not be the best (cheapest) choice for Sunday racing. They do run a very good winter regatta, 1 Sunday a month for 4 months may till Aug. This would be a good way to get started.
I would say BYRA would be a good choice. I know both BYRA and ASC would have storage issues but BYRA has better access and rigging area if driving your board to the club. BYRA has previously run WOD regattas and had a sailboard division for a short time. PCC has access/ parking issues at the best of times.
That's my 2c. Unfortunately because of uni workload I can't see myself doing any regular racing until a) I find a D2/ longboard and b) uni's finished.
Another outside the box idea would be RMYC. They are always looking at getting a small boat program going, but in the long run BYRA or ASC would offer the easiest integration.