Plenty of beach areas that are not filled up. North of Lauderdale or even south on Hallandale Beach will be fine. Remember all the beaches are public, even the beaches in front of $40,000,000 homes on Golden Beach are public beaches. No spring breakers there, just need to get a ride (rental car or uber) to the beach access points. Unless you want the beach with walking to and from restaurants and bars, those areas would be busy.
Only other negative is more traffic and some higher hotel prices.