MO, Aria and the rest of the City Center project are mid-strip; I've found that the elevators to get access to the street are sometimes not working, and the escalators have been inoperative even more often. So if walking is a problem, you might rule out the CC.
Although at MO, if you take the elevator to the ground floor, you can make a short walk down the edge of the exit driveway to the Strip without having to negotiate any further stairs, escalators or elevators.