If you take Amtrak, be it Acela or the regular trains, you will have to stop and transfer at Penn Station in NYC. That will add quite a bit of time to the trip.
I either drive or use Amtrak when I go to NYC from Northern Virginia. I couldn't consider either option to get to Boston. It's a one-hour flight from either National or Dulles, so for scenery purposes get to Logan, rent a car and head north from there. New England is really nice in the summer.