Hi Bill,
It's nice to see you are so enthousiastic about visiting our little country :-) Here's two more ideas to consider:
#1 I'm not sure if you'd feel comfortable driving in a foreign country, but if you really want to see the Afsluitdijk, you could also rent a car for about €150 for a day (much better than the €250 p.p. for a daytrip you mentioned earlier). Driving around Amsterdam is a bit tricky if you're not used to it, but you could consider taking a train to Schiphol airport and rent it there, the airport has easy access to the highway. From Amsterdam to Leeuwarden accross the Afsluitdijk is about 150km one way. The added value would be that you could also see a bit of the countryside in Friesland. As Arizona says the landscape is very different from the more urban area's around Amsterdam, it's very green, flat and a lot of farms/agriculture and cattle breeding.
#2 another nice day trip from Amsterdam is to visit the island Texel in the north (here's English language info about the island http://www.texel.net/en/). You take the train to Den Helder which takes about 1h15, then the bus to the ferry station where you find the boat to the island. The boat ride is only about 20 minutes, but it's a nice trip. Then on the island you can travel around by public transport (bus) or you can rent a bike (I think for a day the rent is about €8.50 p.p.). A return ticket for the train is about €25 p.p. and a return ticket for the boat is only €2.50 p.p.
Have fun in the Netherlands!
Lisa