As I recall from trying to walk along the beach from Grayton Beach State Park cabins to old Grayton Beach, Gulf Trace was about the only development between the two.
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I think you're right. The beach there is never crowded, and if you go east OR west from Gulf Trace you can be all by yourself most of the time. The beach is also wide, which is nice, and has a gentle slope. For people like me who put the sand chair at the edge of the water and read, it's perfect.
On another note, dear Hop taught me to surf when I was down last at Dune Allen. Later I went to Gulf Trace while he was at work, and the waves were even better. It was shallower out to the sand bar, for one thing. Don't know if learning to surf is an issue, but I recommend it...