I agree, if you're going to spend time on the Mall, the Hyatt Capitol Hill is just fine. They did a complete room renovation a few years ago...and diamonds usually get a full suite. I don't know how you're getting to DC, but the hotel is just two or three blocks from Amtrak's Union Station.

And, as I'm sure others will tell you, you need more than "part of a day in the Smithsonian."

there are close to a dozen smithsonian museums scattered across the local area. Part of a day will barely let you see the best of one! If I had to pick one, I'm not even sure which one it would be!

http://www.si.edu/museums/