I feel like something is wrong with the collector upgrades because their inventory was suddenly back to 5 at some point and their speed just went down from 2.6 to 1.9 when I upgraded it. Not sure when this happens and why.
Fun game, but after a enough speed and inventory upgrades, what was slowing me down most was having to wait for the animation for selling materials at the shop to finish before I could sell another batch . Maybe it should be more of a purely visual thing, or some way to speed it up, though it takes a while for it to become relevant.