Blood Mage is a weird skill. It's either over powered or under powered. I'll confess to not caring for it much in its current incarnation. One way to make it a little more appealing and, at the same time encourage people to actually level up the skill, might be to make the Stolen Spirit and Stolen Soul buffs stack, say 3-5 times. That would improve the skill's magic power bonuses and its ability to harvest mana in the middle of rollicking, room shaking AoE combat. And it fits the theme of killing things for extra profit.