I agree with your Hubby -- I would avoid DC, unless you absolutely wanted to see the Smithsonian and/or Monuments, or Arlington.My hubby seems to be warming to the idea of a train vacation, even before we retire. (Plus he's getting REALLY tired of not being able to go anywhere on weekend day trips!) So just before the weekend, he suggested that the two of us take a week off this fall for a train journey. If we go East, he'd like to visit Gettysburg and Mount Vernon (but NOT DC). Plenty of time to research such a trip before actually booking it, at least!
I would look into the Frederick, Charlestown, or even Harper's Ferry areas. Lots of Hotels and, and you could tour Antietam, Devil's Backbone Park, and Harper's Ferry in addition to Gettysburg.