Thank you for the extensive feedback! You really hit great points here. The auto picking is important to reduce tedium, as it will be only annoying after you did it a hundred times. Still, i feel like i need the manual bit to really drive home that you have to work on adjacent fields. But pro players shouldn't be incentivized to make the game less enjoyable by saving these resources (which you really do feel in the beginning of the run) - optimizing the fun out of it. The skilltree idea would work great though!
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.