Yes, it seems unlikely that the same car could be re-used for multiple trips. However, you could move the parking lots far away from the places people want to go because the car could drop you off at the door and then valet itself to a remote lot. That would at least free some of the very valuable space currently used by downtown parking lots.

Nobody is talking about replacing a car part of let's say 100 with a car park of 5. If we could just replace it with a car park of 50, which with current travel patterns is perfectly reasonable, that would be a tremendous gain.