Yea, I imagine it could simply be the first upgrade you have to get, that is literally the base of the skill tree. While I was writing that comment, I did kind of realize that teaching how to target resources in the way you did was actually very elegant. And now that I think about it, the thing that eventually made me buy the auto-picking upgrade was when I bought the sight range upgrade, saw that that unlocked another sight range upgrade, and thought that maybe there was another more interesting upgrade hidden behind the auto-picking one. I think if you were to take this further, probably a skill tree that shows the player "hey, you have to buy auto-picking, but it will be the first in a long line of upgrades" really would be the perfect solution.