I don't know how others have done that, as I only seem to fet about 700 to 1000 dollars overnight while the game is off. I do know that praising them peeps when they work makes them more likely to work and that does seem to affect the overall wealth level. Also have you clicked the gree $ sign in front of the money? If you leave the money alone for a couple days it really builds up fast. Unfortunately I like to buy stuff like the minor upgrades too fast to build up any interest.

I sold my collectrions when I had a good many coins and twigs, so I got over $6 in a hurry too.

Also there might be a few beta testers out there who got the game a bit early to report back any bugs on the final product. If so it would be nice to find out how many days it took to get to the level of earnings.

Plus there is one trophy for "Won the lottery" so I suppose it is possible to get that as an early event and have loads of money for upgrades.