<-- Not the best at explaining or with Mage stuff
I've never really gotten into playing a Mage so I'm hoping one of the higher level Mages can help out too. But let's see... if I was to play a Mage and go with the skill empowerments it'd go something like this:
1. Max Cooldown on MM
2. Max Damage, Cooldown on Firebot. Possibly some points into SP Consumption
Then when I get to Magic Burst, since you're full INT, you're more likely to be in a party so SP Decrease on the skill (so you can cast more before you have to use a stone/pot) and possibly some into cooldown. Look at the skill empowerment window and judge how much you'll need.
You'll get Magic Blast at level 49/50 (forgot which)... and that's when you should use SP decrease on the skill. Then just save up points for Nova and Inferno.