But in an economy one side's costs are people's income. It's an economy, not a household. Money circulates and performs work when it does, like water. What kind

But in an economy one side's costs are people's income. It's an economy, not a household. Money circulates and performs work when it does, like water. What kinds of mills should it drive? A good health care system seems to me like a good candidate, since it fulfills the most basic needs of humans after food, warmth and shelter. Also, you assume "all other things remaining equal", which is unlikely.