Head-to-head, Ullrich was never able to sustain it with Armstrong, and I think the consensus is that cadence had a lot to do with the American's dominance. As I understand it, Ullrich once tried to ride with an increased cadence, but didn't feel "comfortable" with it, and resorted to his old technique. So, really, the argument for mashing just doesn't hold.
Increased cadence does require a certain conditioning of the cardiovascular system, but once that is achieved, and the habit is formed, riding long distances with a higher cadence will reduce leg fatigue (in my experience).
Higher cadence also is very advisable for anyone who has suspect knees.