Looking good. I have found decent last minute rates for DC at AAA.
Did you consider taking the Ducks tour? You might really like it, but we haven't had the chance, yet. It is a busy time around here, then.
Sorry about the concert. Are there other groups you like? The military groups also perform often...
The Smithsonian Folklife Festival is also during the time you will be in DC:
2008 Smithsonian Folklife Festival