Wuchie - FWIW we just returned from Seagrove. Our house was sandwiched in between two public beach walkovers and there was absolutely NO space issue or beach drama whatsoever. There were about 6 beach vendor chairs/umbrella set-ups each day and the majority (gasp!) was non-beach vendor set-ups. Everyone spread out with ample space - one row deep with some gaps - and everyone seemed to be having a good time. You won't have any issues - go have fun!
But I know - I too had the audacity to suggest beach vendors were a nice service for those of us who are visiting and don't / can't bring our own beach set-up (had a few dislikes from this crowd for saying such a thing and suggesting from a visual standpoint they look nice - it is the photographer in me, what can I say).
Personally we always avoid high-season and try to avoid crowds at all costs. We'll never stay in any place with huge condos or during peak weeks, etc. I'm there for the beach, not to be annoyed by other people - I get enough of that at my day job.
It has been a few years since we were there as we can't afford to go every year. It was nice but busier than expected. I'd likely not go again in September. Also a bit sad to see such huge houses taking over everything (We stayed in a 1950's 1200 sq. foot house). I get it, it is all about the $$$ - everything is, especially in a tourist town.