Saw loads of Senators games at RFK from 1966 until they departed for Texas.
Always parked my car within a stones throw of the stadium, bought a Gen Admission ticket and was seated in a nice box seat near the field a few innings later. The "ushers"were totally non-caring/oblivious. Several thousand people rattling around in the place, what did they or anyone else really care?
My dad and I did the same before I went off to college in 1966. Yes, the parking lots were a great improvement over Griffith Stadium. We usually got the PEPCO box seats in the mezzanine. Great views, and we were amazed that we could order cokes and hotdogs from mezzanine attendants.
Otherwise, I thought the best seats were in the upper deck behind home plate and spread toward 1B and 3B. The upper deck was rarely full, so fans could crowd down toward the railing and see everything.
I think DC Stadium was the best of the 1960s ballparks, the baseball-football parks. It was shaped better for baseball, but also made a great football stadium. The others -- and I saw many Met games at Shea -- were circular, leaving baseball fans a long way from the game.
(Ah, but nothing matches Griffith Stadium for watching the game. Upper deck seats felt almost like they hung over the field, but they were high enough that the box seats below had a full view of those homers by Roy Sievers or Harmon Killebrew.)