A better mixture of fast and slow court tournaments would be better for the bodies and long-term health of guys like Nadal and Djokovic. So much grinding on slow hard courts season after season can't be good for the players' joints.
Probably the most ideal surface distribution at the big tournaments was from 1975-1977 (even though the Aussie Open was a lesser major then). All 4 majors were on natural surfaces (2 on grass, 2 on clay) and the two biggest non-slam events, the Masters and WCT Finals, were on indoor carpet.
It's a shame that hard court events would soon proliferate and become so dominant on the tour.