There's no bonus for beating levels in fewer moves as far as I'm aware, as long as you're not going for the Grandmaster Flash achievement. So once you get right next to the open door at the end of the level, use up the rest of your AP destroying large sets of blocks for experience and to charge your magic meter. This can also heal you if you have the Ring of Restoration.
The best way to get a lot of experience is to buy the last armor ... with this, you don't get hurt for making moves without AP is -> now collect EXP as long as you want.
