I've noticed they seem to level up after X uses. If this is correct, how many uses does it take to get the next level?
To get from level 1 to level 2 you have to use the power 15 times. To get from level 2 to level 3 you have to use the(level 2) power 30 times. It appears using the level one power does NOT level up to level 3 - once you've reached level 2, you have to use level 2 to progress.