A simple power washing of each stations concrete, a simple one color clean paint job of the walls and ceilings on each platform, and replacing all broken lights with LEDs. Let's make Metro feel clean, open, spacious, and modern by tiding up our stations!
I will even donate my time to help power wash my local station (Stadium Armory) if given the chance. Enough of the dust, dirt, and dark cave like feeling of some of our platforms. Let's just get a maintenance crew who's sole job it is to go from station to station and keep it relatively fresh/clean/up to date. (I'd also suggest replacing the brown signage with something a little less industrial and more modern).