Around that same place is Emma Wood State Beach, Hobson County Park, Faria County Park, Park Number Three (Ventura), Carpenteria State Park - very close to where you saw people parked. You can use your generator - until the time on the sign above.
I have stayed at Rincon a few times. I like it better than Emma Wood State Beach. There were a few times loud motorcycles would drive by, but the train is fairly quiet and you can't hear the 101 from Rincon. I have not stayed during the summer, only off season. If your looking for a great place just north west of Santa Barbara, check out Jalama Beach County Park.
The train is loud at Carpenteria and the 101 is loud at Emma Wood - not horrible, but not my favorite places.
