I believe there is a lot of ppl who already said this, but maybe an achievement that is completed after you bought all the managers that show the cash per sec for each business. And the reward is a global cash per sec.
There is the last mission on The Mine Collapse. Where you need to find 8-bit pickaxe, because of the limited amount of uses, and the poor guys wants to make a square hole. I got the same problem in my mine, you know, on minecraft :D