...instead of expanding the number of seats, they can put better more comfortable seating in and replace all the hard benches, etc. Keep the number of seats the same but make them a litttle more roomier and comfortable so the game experience increases. One of the attractions of staying at home and watching the game in HD on your big screen is that you can be comfortable in your favorite chair etc and not have to be elbow to elbow with some guys knees in your back and having people step all over you to get past on their way to the bathrooms, etc.
They could even get away with charging more for the upgraded seating. It would significantly improve the in-stadium game experience for the viewer.