No physical changes I know of, other than some concourse improvements, and replacing the two-story restaurant cylinder in the historic hall with a coffee shop window. The powerful Commission of Fine Arts had a report that said it disrupted sight lines. Exclusive parties are the only functional use of the main hall.
The very popular mall-with-a-movie-theater era ended with the same issues as other malls: economics and feeling safe. As far as I know. And likely mismanagement.
I recall the remnants of the Bicentennial era, trooping around the perimeter of that pit on wooden catwalks to get to the trains. Last month I ran into some Italian tourists who had logically taken the corner stairwell, under the big letters "Stairs" in the main hall, to get to a Flix bus. Upstairs it puts you out in open restaurant seating, from which it's hard to find the walkway to the garage. Nice view of the backs of the Centurions though.
Late at night and early morning, workers check tickets at the entrance to WAS. It's open 24 hours. They were checking tickets when I went in for the first train of the day. I had parked at 4am, and gone for a walk around the east side of the Capitol. They didn't check my ticket coming into the station proper from the parking garage, but at $25 a day I guess you get privileges.