Old, but first!
Let's not forget that IAD may reflect its age... but it was the first of its kind! (IAD, of course, was the first airport in the world specifically designed for jet aircraft.)
Personally, I find a great deal of American charm in IAD. It takes me back to the 1960's-70's movies you now see on Sunday afternoon television when air travel was a luxury and everyone envied the opportunity.
And, by comparison, let us also take a look at America's other major gateways... BOS, LAX, JFK, EWR (terminal B)... all bare a striking resemblance to IAD.
America is all about nostalgia... IAD serves our country well in that regard!