Haha awesome, that's so cool! :) BTW I love that you bought so many Wizards - I do that too! I really like the magical spark flying from the Wizard Tower to the Mortar. I need to come up with more mechanics like that.
I'm thinking of adding ways to upgrade buildings which would unlock new functionalities. My idea was to make each Arcane Overload generate new currency, Orbs, which could be used to other stuff but changing units into new ones is a cool idea - I'll think about it. :)
Summoners could summon some creatures that shoot fireworks and disappear after some time and you could upgrade how many fireworks those creatures shoot.