I didn't use many offensive spells. I found a Burning Wall spell book in Mardaneus' house which came in very handy in a couple places early in the game (the spider at the bottom of the catacombs and the heavy orc just south of Aleroth), but that's about it. If you have the skill points, you can save the game, learn Deadly Discs and try it out.
Kiya described defeating the vampire in the cave using Deadly Discs; she cast the spell repeatedly, which knocked him back behind his coffin and killed him there, before he could even get close.
