Lots of things affect price of waterfront lots: Distance to the Gulf, river, Matlacha Pass or Pine Island Sound. One key factor is the number of bridges and the height of the bridges that your boat must pass under. "Sailboat" access is considered to have no bridges blocking the mast for instance. Depth of the water going out can dictate the kind of hull that your boat has and therefore affect price of the waterfront. Also the direction that your lot faces can also affect value, as southern exposure is highlly desired to keep pools their warmest, to provide summer's breezes, and to allow the house to block the lanai from winter's northerly cool winds.
I've lived on the water here and boated here for 17 years. Plus I worked at a yachting community (Cape Harbour) for 10 years. Call me for more info and to answer any further questions you may have.
Sam (Rosa) Yaffey
Century 21 Sunbelt