As noted, this is a very quick trip, given the distance. A couple of thoughts:
>If you can travel in March - May or September - November, you'll avoid many of the crowds as the kids will be in school.
>You will have an option of a coastal route or of following the Blue Ridge Parkway. No, they're not like mountains in the west, but they have a beauty all their own. If you take the coastal routes, be prepared for heat and humidity in the summer in the south.
>If you do a fall trip, start in the north and head south, following the changing of the leaves. Be prepared for a lot of company on the trip.
>If you can carve out more time, definitely plan on multiple days in the D.C. area. The Smithsonian is actually a number of buildings, and there are a number of amazing things to see elsewhere on the Mall, too. The next time we go, we want to spend a week.