The bulk of the ridership will pretty much always be at the rush hours.  I do think they need to scale it somewhat when ridership is lower, but they seem to not be willing or able to do that.  When they moved to the every 15 min for the W, at some point, they also moved to 2 car trains, which made the trains way full on the way to work in the morning.  If they go to an every 20 or every 30 min schedule, I will probably start driving and suck up the parking costs.  As is, taking the train, doubles my commute.