If you want to make money fast, you can exploit that the game uses your PCs clock to calculate how much money you get, when the game is closed. So, before starting the game you change your clock to 2060 or whatever. When you now start the game, you should have a lot of money. Buy upgrades and leave, then reverse the clock. Money and upgrades should stay, but your power boni are back to normal.
Rinse and repeat.
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