Perhaps it should be both a learnable skill and a quest reward, like Restoration. By learning the skill, you essentially open up the ability to use every spell, but only if you find it lying around. So do you risk putting five points into a skill that has random accessability?
Runes shouldn't be too rare. After all, Fire Damage (5) is only about 30 damage (I'm guessing here). You wouldn't kill an Orc with that. They'd be handy with the Know Creature skill as you could judge their resistances, or rather their weaknesses.
Another idea: a rune called Enchant. Combining an Enchant rune with other rues allows you to imbue different magical powers into a charmable weapon.
(Enchant + Fire + Poison) on a Weapon with Charm Quality 3+ = Fire Damage (1.5) + Poison Damage (1.5)
(Enchant + Heal + Heal + Heal + Fire) on Armour with Charm Quality 5 = Survivors Instinct (6) + Resist Fire (2)
By this method, you shouldn't receive any spells by using enchanting equipment. Enchanting an amulet with Elemental Strike (8) would be overkill! Instead, they should give passive benefits from other classes. Or is Survivors Instinct (8) overkill too?
