I read a fun book once that proposed we should go off the gold standard and go onto the plutonium standard. Plutonium loses value as it decays, so you have incentive to spend it. If you keep it too long, you're likely to get cancer, so, again, incentive to spend it. And if you collect too much of it all together in one place, it goes kablooey, so there's one more factor limiting wealth hoarding.