I just read one idea that I really liked! I just want to echo that idea here.
So how about this, A new world, but one that has no connection with the main game whatsoever. The point of this world would be to gain more experience for your pets.
It could even be a world in which you play, not as a wizard but as your pet, and instead of battles, our pets would gain experience through mini games. Or, each pet would get a custom set of spells depending on it's school.
Maybe the final reward for completing this world would be an extra talent or an extra pet derby skill.
However, each pet can only go through that world one time. So if you have 5 diffrent pets, you could go to that world 5 times, for every pet.