Spring Break in DC

For 2010, I've decided that the adventure part of my identity needs some attention, so I'm going somewhere for Spring Break. I've decided to go to Washington DC, as I've never been and have really grown to appreciate our political process and common history. Here's what I've got scrapped together so far:

When: March 11-16, 2010
Where: Washington DC
Details:

• Depart Thursday, March 11 around 9pm to catch the midnight Amtrak Cardinal from Indy to Union Station. Spend the night on the train and the next day observing the beauty of the Appalachian Mountains from railcar. Arrive on Friday at 6pm. - $59 for coach, 18-hours in transit including 1 night.
  
• Check in at Hosteling International - Washington DC, which is 4 blocks from the National Mall. Set up home base for the next 4 days, find some grub and walk around for a while. - $30/night in the dorm.
• Saturday-Tuesday are pretty open- I would be content to spend hours in the Smithsonian and the National Archives. Of course, there's all the monuments, and I suspect I'll spend plenty of time just chilling in the Mall.
  
• Gilberto Gil (last.fm), the former cultural minister of Brazil and Creative Commons advocate, will be performing a concert on Saturday night at George Washington University - this would be super awesome. Seats start at $35, but I think it would be an awesome experience.
  
• Leave DC around 5pm Tuesday, March 16. Catch plane from Baltimore to Indy. $9 for Amtrak to Baltimore, $78 for BWI->IND direct flight. Arrive around 10pm.

Overall, I think the plans look good. I'm very excited about travelling by train. The hostel is insanely convenient and includes free breakfast. A cheaper place would likely end up costing more due to transportation and lost time. I chose a flight back because the train would cause me to lose two days - it departs on Wednesday at 11am and arrives Thursday at 5am, after which I would just sleep all day. It seems the base for this is around $270, including lodging, transportation and breakfast. Most of the monuments and museums are free, so lunch and dinner would be the major incidental costs.

Does anyone have any tips for DC? Any places that you would or wouldn't see? General critiques?