The main difference is that PoS doesn't waste a bunch of electricity in doing so.
No, the main difference is that consensus is formed by those holding stake and not those willing to work. To me it is the difference between rent seekers (PoS) and innovators (PoW).
The miners' eternal vigilance is the price paid for freedom.
This
One cant emphasise this enough, to experiment safely one could spin-off the blockchaine into a NXT clone. The predicted outcome will be the paradox of thrift, as holding capital is reworded, where as in Bitcoin holding capital is a risk that increases or decreases according to the state of the economy.
Understated but important are the myriad of speculators creating a free market force who perform the same function as the FED as they try and control the money supply by selling high and buying low. In contrast PoS rewords give advantage to those with capital and leave those without vulnerable to rent seeking, (more realistically seeking a PoW alt.)