Ooh, I will have to check out the Spy Museum, sounds like fun. And yes, Mount Vernon is lovely (my neice and nephew only live about 5 miles away from there). Have you decided how you are going down yet? Although the ride on the Cape May-Lewes Ferry is very nice, it really is way out of the way for you. The quickest way through NJ is to just take the turnpike or 295 straight down. Were you planning on seeing any of the historical buildings in Philadelphia? I am not good at suggesting fun things, but if you have any questions. I hope you have good weather and a wonderful trip!