This is less of an idea but more on balance, It took long between each new building type to build and for me to see how the new unit acts, i would consider changing the cost of buildings to start cheaper but gets more expensive by each building built in the same category, So the initial 3000 + 40 cost of machine gun hamtah felt steep at start even for incremental games, maybe starting at 1500/2000+25 blocks then going higher in price each time built would urge the player to stick around to see the next building!
Another thing is maybe an "end run" button that lets you keep whatever hamtahs you didn't use yet in the run and take them home if you felt the run isn't going well.