Hi Debs,
Naples is really really nice, but really really quiet
Ideal for couples, or very young children but may not be enough for your son to do, other than the beach.
It's a really classy/exclusive place, we have been twice once before Joshua was born and once when he was very young.
The problem you may have overall is many of the places I suggest, are probably not ideal for a 9 year old. I guess ultimatley that's part of the reason we haven't been back - it would feel like taking Joshua away from the fun, and with his autism he hates change also.
I think the concept of a few days is a great idea, but at your son's age it is difficult getting the balance just right. Clearwater/St Pete's may after all be your best bet, Busch Gardens is easily reached, the beaches are good and I know there is other stuff to do also - there is for example a nice Dolphin aquarium at Clearwater.
Sorry if I have moved you away from your original ideas, I have a habit of doing that!