I think if the ball is deadened a bit, then the importance of steals will go back up for sure. I mean, it's not hard to understand why.
Further, speed means:
- ability to take an extra base when a player has the base-running skill
- extra pressure on the defense, as players have to make throws accurately and catch overthrows, bounces, all the other odd-ball things
- ability to leg out hits or even to make them close enough that a defender hurries, adding chance to a double-play
- ability to cover more ground in the field, both infield and outfield