RE: Vibrio Vulnificus
Yes, you can take a sanding block and put a flat (better still a tiny radius) on the traling edge and tip of your formula fin without affecting the performance of the fin to a degree you will be able to tell.
We've been "blunting" the TE of fins that "whistle" for years with no affect on the performance.
Run the sanding block (with 240 or 320 grit abrasve paper) down the TE of the fin with the block perpendicular to the fore and aft axis of the fin. 2-4 passes down the fin will take the sharp edge off. Then turn your sanding block to a 45 deg. angle and "break" the sharp edge where the tiny flat meets the foil of the fin. Just once or twice down the fin and you will have a nice 45 deg. chamfer that won't cut you if you happen to rub your leg or arm against it.
As far as sailing in Ft. Myers, (at Sanibel Causeway) you can ususally get away with a vertical fin is you go out and find out where the deep areas are and which areas to avoid because they are shallow.
At Pineland (on Pine Island) the water is much shallower, so anyting larger than 40-42 cm will be a problem.
You could run a shallow water 40 cm fin, but I've found the Tangent Dynamics Reaper 42 cm weed fin to work very well in Pine Island Soun.
True Ames has a Shallow Water Weed design that I use as well.
Hope this helps,