I agree, more players playing the game is always good, but it's tough to keep them playing. I am not even sure an in-game incentive system would be successful.
Tutorials can only teach so much, the pressure of a real match multiplies difficulty, there's no way to duplicate this without practice unfortunately. The best tutorials would help players get over the first humps of execution and strategy.
An opposing character tutorial might be good, something that gives players an idea of how to play against other characters. Not matchup specific tutorials, but just an opposing character tutorial where you can play any character against them. For example, the tutorial goal might be to successfully defend against a bnb, and then react with an combo that does a certain % of damage, something that requires some experimentation on the part of the player.
Or, maybe even a practice mode tutorial which shows players how to recreate different scenarios to practice against.