Im glad you found it helpful :)
i had one other suggestion that's more "feature suggestion" than feedback and i avoid those, but i was still thinking about it so ill mention it. something that might help with a lot of stuff related to "miner upgrades" could be do like you did on your "simpler space" game, and separate into more categories of miner blocks, to encourage designing a ship (like cargo block, magnet block, armor block, insulation block...)
more categories would make your "cost scaling" harder to balance (i think right now it individually scales price per-category for each of the 3 categories?) but maybe it would work if you remove cost scaling completely and instead make each part have a weight stat and make the total ship weight affect fuel consumption, because its heavier? something like that? so theres still a cost penalty for having too much (need a lot more or better fuel storage and ship works less efficient) but it doesn't punish as bad for experimenting
it was fun playing around with designing different ships in simpler space and trying different strategies even just for fun (mine laying builds were fun). in this game at the very end after I had everything unlocked and a ton of money I started to experience the same thing, the bottleneck started to be coal because I couldn't smelt things fast enough so I got to think about which parts would be best to get the most coal as fast as possible on a run
heres the final ship i ended up with (after breaking bank selling things for 51x value from the bug) https://imgur.com/a/odtDxVo
EDIT: for sells price bug, i think you set it right? maybe?? not a spreadsheet balance thing, something in the code... on sell button, "topaz gem" shows $1,000, and "rose glasses" shows $1,250, and when I check your code the function where you set item values it matches there (i see they say 1000 and 1250)
problem is when you actually click sell, jewelry items (glasses, earrings, rings, necklaces) make your money go up by 51x the listed value instead (but it only multiplies the jewelry, topaz still only gives you 1000) i have all the researches and full museum, idk if that matters