Even if the new upcoming combat system will make the Recruits mostly useless, i still want to suggest a new building that can be accessed by players how reached level 50: a new copper mine, that acts like a lvl 5 normal copper mine.
We already have upgrades for wells and grain fields, why can't we add an enhanced copper mine (that can cost the exact amount of materials as a normal copper mine plus upgrades, with half of the construction time of the total time needed to build and upgrade a normal copper mine).
I know the Endless Copper mine exists, but this idea is to make a better flow on copper mining, as a copper vein disappears in less then 8 hours (4 with the speed from research) with a full upgraded mine, and then we have to repeat whole process again.
Or simply add more copper veins.