Sure!
Making it more D&D-like would be great! Also, being able to buy items which do special attacks, being able to buy special abilities (or spells for specific pet types), more battle options, different battle locations/backgrounds with different effects on the battle, NPC Petz (e.g. a dragon) created by the admin which could be challenged by people when they get high enough in level (with appropriate awards), more customisation of your pet, ability to wager on battles taking place even if you're not involved, better pet graphics (or allow user to submit own graphic).
That enough to start with? I'm sure I could come up with a lot more!