I was there about 10 or 15 years ago and enjoyed it very much. Most planes have since moved to the big U-H facility at Dulles. The following link states that Silver Hill is closed to the public.
http://www.nasm.si.edu/visit/
A friend of mine spent time researching things there. He just told me a good way to get your foot in the door is to open a dialog with one of the professional research staff (e.g. captured aircraft archives). You could schedule a visit to do your own research for a half day. Maybe you could ask for a tour while you're there. I'm not sure how much is really there now.