My info is from some research, and info from other treasure hunters, not from anything I found. I know there are hunters in the area, but seem to be beach hunters looking for today's jewelry. I now live in NC, but grew up in SW FL. Still visit and hunt a few times a year. SW FL certainly has seen lots of activity for centuries. My wife's ancesters were some of the 1st permanent (non indian) settlers of Sanibel, after the Civil War.
1. Check this site:
http://www.floridadetecting.com/index.html for a contact.
2. I found several brief web references to a shipwreck off the north end of Naples (no exact location, but that locals found old Spanish coins for a few years...
3. Ignore all the local legends of pirates around Pine Island sound. They excite tourists and local restaurants promote the idea, especially Captiva Island. It is certainly possible some were in area at some times, but the local legends have been proven false.
4. Early Spanish ships did hug the coast when sailing from Mexico to Pensacola, then south through the keys... surely some were lost or were run aground. There are local references to crew members shipwrecked along the coast.
5. Ponce DeLeon did land a large army at Port charlotte and move on land north thru Florida. The Port charlotte area was used by Spanish for many years.
6. The area around Carl Johnson park (south of Ft Myers beach) and the small keys in San Carlos bay had Indian mounds (which you cannot hunt!) but there were rumors of treasure found in the 70's (i lived there, and some of the keys were literally bulldozed by some treasure hunters.
7. There was a trading post on the south tip of Cape Coral in early settler days. It shows on some of the early maps. Never checked if it's been found. Some historical references to an early massacre by the indians in very early days.
I would be interested if you find someone who's actually found something that old.
Some of the early maps that can be found online will show the early settlements and the shipping routes. Also - local divers clubs may know the position of local wrecks.
hth