It may be that society really does become blade runner and we spend in "credits". but we'd still need to know the value. The problem I find is the volatility of it at present. Iy could mean that you can afford a full tank of diesel one day but not the next (as an, excuse the pun, crude example).
There will have to be one singular unit as a reference point, I believe.
Ya agree with your points! And specially the volatility is a big issue in that decision, since the fluctuation in your example with the dollar price happened in the last decades not because of reallife time events more as a result of a debt base money system in which the central banks can print as much money as they want. And even if they can adjust the interest rates and force companies to spend their money, the could raise it by few % each year again and it will end up in another dept crisis. See this chart: http://money.visualcapitalist.com/all-of-the-worlds-money-and-markets-in-one-visualization/
After all i would suggest the question Should the currency be centralised? is our first big question (1)