Self driving cars could encourage sprawl by making commuting long distances more practical. If you could be working during your commute instead of driving, and didn't need to find parking once you arrive, a 2-hour commute could become practical. That would intensify the "car culture" that currently drives municipal planning, but would reduce the harmful effects. As you mention, less space wasted on parking, less congestion etc.
On the other hand, driverless cars will be a big boost for Uber, Lyft, Zipcar, GetAround and the like. That could make city living more desirable, because car-on-demand only works well when there are lots of available cars nearby. Folks that live out in the boonies would still have to own their own cars, and so wouldn't benefit as much from the technology as city-dwellers. Also, spending less space on parking has a bigger effect in the city where space is already tight, so we might see even higher density in the inner city.