I must've missed this topic when I was in New Orleans for Super Bowl. ; - )
Don't bother with the bus. It runs once an hour, although it does stop at the mall which is near the Holiday Inn, but it's slooooooow. You could catch it into the city and the cab it back to the hotel, or from the Hampton Inn, it would be about a 35 min walk to the downtown area, and then you can cab it back to hotel.
As long as you don't plan on drinking, Frederick is easy to drive to like others have said. Cheap parking is plentiful and there is free street parking on the outskirts of the city.