Sincerely i don't know why people find this UI confusing or too complex .__.
I mean you just have a tab for each game mechanics and the shop on the right what's so hard ? if you wanna buy upgrades you don't have to "click around 4-5 times to figure out what upgrades are available" as i could read, just click on the upgrade tab and the one you wanna buy ...
Or maybe i'm not far enough in the game to see those problems but for me there isn't any. Good job Divine Games ! :D