Wow, thank you for playing and writing this post. You raise a lot of good points, I agree with pretty much all of them.
I'm working on balancing a game (broken auction system make it harder to add new drill part as well). The ability to have 3 drills is added in the last minute (that's why it's not a research) so it look pretty weird and hidden, I'm working on that too.
The progress... yeah it spikes. I playtest it a bit and skip from standard set right to cyber set. I'll try to adjust that, but it would take a lot more playtest to make it right.
Sells price, yep I didn't think too much when setting it. I think I need to create spreadsheet now.
Also button for more control when digging, I'll be adding that too.
Thank you again for playing and writing such a detailed feedback.