Really, the national venues have had really interesting stuff if you know where to look. Representing Northern CA's Arden, i've been to 3 nationals competitions.
Washington D.C. - obvious (I would like to say that the Lincoln memorial at night is unparalelled)
Witchita, KS - the competition was held during the riverfest (big city fair) and if you spent some time down there it was awesome. Also, a few miles out from wichita in Hutchinson was the Cosmosphere
www.cosmo.org, a Smithsonian afilliated space museum with absolutely phenomenal displays (the actual Apollo 13 command module, an SR-71 blackbird that they built the building around, the Liberty Bell 7 Mercury capsule, just to name a few). Upstairs they have an astronaut training program (the door was unlocked so we looked around) with a full size space shuttle simulator, mission control, and other capsules that you can go in and work with.
Bloomington - Indanapolis was holding trials for the Indy 500 after the competition.
You really have to find the little cool things in the cities, explore a bit.
