Thanks! Yeah, you can upgrade the towers with 20 wood/stone, 2 corpses & I think 30 or 40 gold, I can't recall right now. The first upgrade speeds up the fire rate and the second upgrades the damage output per shot. I definitely plan to add more active combat if I come back to the game with the player getting spells and having minions that would have follow the player around and would auto-attack nearby enemies. My eventual plan was to make the enemies more intelligent to where they'd actually attack the towers themselves and you'd be actively defending your towers as well to a degree.