Dave,
I have to put in my two cents for the Great Lakes State--Michigan. This time of the year the weather is usually nice and there are plenty of lakes and other activities. In the Detroit area there are plenty of sites. You can tour an automobile assembly plant at the Ford Rouge Complex (that is if they are still building cars there next year). Greenfield Village and Henry Ford Museum is a great stop. The Detroit Institute of Arts is another great museum. You could even take in a Detroit Tigers baseball game! Additionally, there are many family friendly resorts in Northern Michigan. The Traverse City, Charlevoix, Petoskey, Harbor Springs area of the state is amazing and is beautiful this time of the year.
For those who have never seen the Great Lakes, it is truly amazing to see a body of fresh water where you cannot see across to the other side! You could also go across the border into Canada--perhaps Toronto to add yet another country to the vacation list. The Toronto Science Center is a great stop for the kids and Toronto is not too far from Niagra Falls.
If not Michigan, Chicago is also a Great Lakes destination and there is a lot to do in Chicago. Also you should be able to get a non-stop flight from Orlando into the Windy City. For the kids, Chicago has the shoreline, the Shedd Aquarium, the Museum of Science and Industry, the Field Museum of Natural History, the Art Institue of Chicago and the Navy Pier. For you and the Mrs. there is plenty of nightlife. You could also take a trip by automobile up into Wisconsin along Lake Michigan.
I would be happy to forward information if any of this interests you. As everyone has pointed out, you have a lot of options!
Tim
PS: I feel like George Perrot--the Michigan guys will know who I am talking about. Sadly, I cannot find any internet references to yet another one of my childhood TV memories!