Two Thoughts:
Grumman Goose: yes, if you happen to already be in the Bahamas with it. Filling those 485hp engines and 160mph cruise (maybe), I would think it would outdo the Commander on one and not the other. :-) But boy would that be cool to land on the water and it would do away with the need to rent a boat. Which might just offset the added fuel you'd need to buy.
The older kids: They'd actually have a blast if you plan the trip around going to islands and renting boats to go snorkeling at places like the caves and reefs. It would cost more renting boats everyday but honestly, the islands are so cool that there are tons of things to do in one spot. I honestly don't like hanging around the same beach all week but had no problems down there because the water was so awesome and they have kayacs you can take out and mess around. Rock Sound is in a round cove of sorts and the water is a lot smoother for things like that.
Either way, I'd recommend it.
Glenn