The point values at Natl Harbor are pretty close to Alexandria. The Balcony units at NH are higher, and the standard units at Alexandria are lower.
But, there is still plenty of availability at both for June and July 2010, except the 4th, which is sold out at both. That's a significant improvement vs. just Alexandria alone in prior years.
Edited to add: my diamond in the rough in the DC area has always been the State Plaza Hotel. Across the street from the State dept. in Foggy Bottom. Units are studios or 1BR with full kitchens. Furniture is *very* dated, but perfectly serviceable, and good rates.
http://www.expedia.com/pub/agent.dll/qscr=dspv/htid=11234