This is a several years old complaint but I would really love it if all the upgrade coin costs in the game were removed. I am not saying this out of trying to gain economy advantage as a player. I would rather have no upgrade coin costs and all of the costs paid off as soon as you get the required duplicates (like if you got 5 pawns, if it would instantly pay the upgrade cost) rather than having upgrade costs as they are now.
I feel like I am being punished for diversifying my army/making collection progress this way. I'm not going to make a Slime+++ if to me it looks like it's obviously worse than Slime++, but even after getting the units I have to pay gold to experiment with it.