jabird Mr. Saarinen may have done a beautiful swoopy terminal for IAD, but they've spent many millions over the years correcting his design mistakes. He clearly didn't understand queueing theory. The original passage for the baggage carts was so narrow that one could not pass another. There was an inadequate number of luggage carousels (4) from day one, but that may not have been his decision. The midfield terminals are one of the fixes. They weren't in his plan. The waiting area beyond security was a fix added years later to the original plan. It is over the expanded luggage area needed to fix the original plan.
I'd guess that the new terminal at DCA will weather its first 40 years a lot better than IAD's has. It's not very pretty from the outside, but I like it inside and it had to fit in a very constrained space.
I must have been in a bad mood the days I used DEN because I thought it a big disappointment. I didn't find any interior place which had a beautiful view of the mountains. That should have been a priority. And how about the shuttle train to the concourses - if it breaks you're stuck since there isn't a walkway beyond the first concourse
AFAIK.