I think you have a lot of good things going for you.

No.1 You can store your luggage in the airport. Charge for 24 hs. is between 4 and 6 Euro per piece of luggage.

No.2 The train station is situated directly below the Airport and it can take you to Central Station in Amsterdam in 20 minutes.

In your situation with only a few hours in town I would go for an hour in a canal-boat trip.There are great views from the water and the piers are not far from where the train will leave you coming from the airport. Then I would take a rest and have a meal,if it is lunch time, sometime typical like a raw herring with onions, or pancakes, or any other local food...or if not an Indonesian rijsttafel.

What I really love in Amsterdam are the Museums, the Van Gogh Museum and the Rijksmuseum and to walk around its beautiful canals, and old streets as well as beautiful up scale shops and markets. But it is up to you if you'll see any sense in going to a Museum at all. You have to know that in the Airport after you pass security there is a free Exhibit of the Rijksmuseum. This year because it is the 400 Anniversary of Rembrandt the exhibit is even better than usual. Do not miss it, especially if you did not find enough strength to go to the Rijks.

Good luck. Graziela in Miami Beach.