If you invert the economy you end up with starving broke peasants, or peasants just growing their own food and not buying yours. YOU may be eating Heroes' Feast every day, they're still doing the same old thing because they can't afford your fancy-schmancy magic food.

A Green Lantern ring is something like a Ring of Infinite Wishes with some minor limitations, really. It's way more powerful than anything you'll find in the DMG.