One of my highest frustrations is that when you're crafting anything (food in the stove, anything in the forge, etc.) you can only do the 9 at a time. I wish there was a way to do stacks of crafting (like stacks of 10 or 25 glass in the kiln, stacks of ingots, etc) to make the process a little less babied. Even if stacks of 5 took 5 minutes, stacks of 10 10 minutes, that would be a major improvement. I say this because so many times I've terraformed or mined out an entire ore vein, only to come back to the forge and kiln and sit there, bored brainless, as the one-minute timer ticks over and over again. At least with stacks of 10, I could drop it and leave and come back.
The upgradeable idea comes in for example, if higher quality crafting places (campfire -> cooking pot -> stove as I've seen in some games) have higher stack abilities, faster crafting, higher quality crafting, etc. Just another thought along the same lines!