I am not done with this project for sure! Turning goats into upgrades is a great idea! I'm thinking of making so you have to eat goats every once in a while too to keep from starving, and have to balance eating them with keeping enough alive to breed. Also making so only some of your goats have horns and those ones can fight back while the other ones are more common and can produce more goats.
I've got loads of suggestions and feedback and I'm going to continue working on it for a while I hope.