There are staves with bonuses to both magic spells and magic damage, both of which should theoretically increase the damage of, lets say, Arcane Swarm.
I have had such items on a mage. Her arcane swarm was devastating. So was the hammer of some random Mercenary who stunned her, and killed her on the next hit. She was the single character I have lost to an identifiable cause of death.
No good deed goes unpunished...