I was thinking that it could be great to use more than one wizard at the same time in the game.
Think about the possibility to bring with you one of your wizards in your adventures. The "main character" could be used directly by the player, while the other would behave like a minion.
You could divide XPs and rewards amongst your wizards, letting them gaining levels while you proceed in your quests.
You wouldn't have to repeat the same quests with both characters.