Thank you for the detailed feedback!
I'm definitely gonna look into making each upgrade feel like an upgrade, like Reverie Requiem pointed out as well, I did spend quite a lot of time balancing the numbers but I guess I totally overlooked the feel of it.
Regarding the grind, the plan is to add more upgrades and content to reduce the monotony of the grind while keeping the grind itself if that makes sense. That's something I'm hoping to also address in the next update.
Also cool bug! Gonna keep that in for now, I love seeing people break stuff in creative ways like this!
The desert plane issue I totally forgot to fix when I added the skyboxes, I was planning to rework the area entirely so I forgot about it, oops!
And regarding the top of the lighthouse, the way it used to work was that the furnace kept burning resources no matter what, and to keep it running permanently, you had to feed it a total of 10k items. I changed it since then to make furnaces required to be filled to advance, so I also removed that sign and system.