I think metro should allow me to exit and re-enter at the same station during a two-hour window for no charge provided I continue in the same direction. This would allow me to run errands on the way home without paying an additional fare. It would similar to a bus transfer and would have the effect of allowing me to stop an get groceries along the way rather than going home and getting in my car and driving to a suburban grocery store.
WMATA already provides this sort of service with its Farragut "virtual tunnel" that lets me come out of the metro at Farragut North and walk over to Farragut West without paying a new fare. If I could exit at Columbia Heights, then I could hit the Target or the Giant and jump back on metro. If I could exit at Tenleytown of Friendship Heights, I could hit the Whole Foods or the Best Buy. I am currently disincentivized to jump on and off, which means an additional trip once I get home.
WMATA is no worse off if I briefly exit and re-enter, continuing on to the same destination.