Not been but Busch Gardens Tampa, has animals and rides and is meant to be great
Sanibel is lovely for a day or two, also get over to Captiva to the crazy Bubble Room for lunch
St Petersburg beach is also lovely and from St Petersburg pier you can do a boat trip and see dolphins. There is also very randomly a rather good Dali museum there!
Naples is ok for a potter downtown (the rest is like any other US town, just way richer) and you can do a very interesting boat tour and see how the other half live
If you want shopping there are decent outlet malls in Fort Myers and also Sarasota (between FM & Tampa)
I have friends in FM, was there in November, been a few times to the Gulf Coast
The Keys are a big old hike as there is basically one road in and out, you can go by boat, I think from Naples
By the way Miami airport immigration is hell on earth especially on a Sunday night! Don't expect to get out in much under a couple of hours