Cool game! It's nice that there are some upgrades to get in between waves, but I feel that the + Damage one is the best. If you get that, you don't really need the +Spears one, since you'll use less spears.
Yup, probably changing values it can get way more balanced but I was doing other things this weekend (T1 has won worlds again kekw) so couldn't really give it proper testing and some of the assets are still placeholders...