He did actually bring more money to Rome: He started an illegal war against Gaul, Britain and a few other places, and used the spoils from that to fund his political ambitions. In general though the caesars did exactly what you said: They adulterated the currency until it was worthless scrap metal. Taxes and public salaries had to be paid in gold, everyone else had to make do with monopoly money. In the end, people just stopped using the currency and were required to pay taxes "in kind" (ie. in goods and services). In order to prevent tax cattle running away trades and farms were made hereditory, so if your father was a shoemaker you were required to be one also by law. This is the origin of the feudal system which saw the majority of europe's population turned into defacto slaves.