I've actually been to a bit further north to Gasparilla state park. Other than a beach and a really old lighthouse, there wasn't much. We planned a day trip and ended up just turning around - the gulf just wasn't very good that day.
Do you like it friggin unbelieveably hot? As in 95+ high humidity? 10++ on the UV scale? As in can't step on asphalt, eggs frying hot?
Do you and your folks burn in the sun easily? I'm rather olive (think less than john redcorn but more than hank hill) - and in mid-july - I'm not swimming for more than an hour with waterproof sunscreen.
The gulf in that time of year is calming down - winter is usually quite rough, towards spring and the beginning of summer it calms down and becomes fairly mellow until autumn. I can't say theres much snorkeling out there, but its open season on the reefs in the keys for that.
Also in the area is cayo costa state park - available via ferry or your private yacht. I recall we wanted to go there but ended up not doing so for some reason.
Looks like a typical FL resort town, so expect a couple local bars, some places to eat, lots of beach and rich mo-fo's everywhere.
Also this is during the start of hurricane season. It's entirely possible your vacation is ruined by a storm.
Also note that this area is within the lightning belt. Every single day from mid-may on through sept, it rains for about 15 minutes in sofla. Its usually a quick thing, it drenches everything with crazy blowing rain and ridiculous lightning about 4pm, then everything is all hot and even MORE humid until sunset.