The vast majority of money in circulation today is already just numbers on a screen. If I recall correctly, cash makes up less than 1% of the value of all transactions. That was old data too, so it's probably far less now. Think of the trillions we've "created" via quantitative easing. The vast majority of that, if not all, is created digitally without printing additional paper money.
Fractional reserve banking is responsible for this to a large degree. Based on the formula [Money Supply=(1/Reserve Requirement)*(Deposits)] you can calculate that an insane amount of money is created by banks from nothing with the Federal Reserve's blessing.
Here's a graph illustrating how physical currency makes up a tiny fraction of the money supply: http://www.sott.net/image/image/1379...he_United_.png
And here's a graph illustrating the money multiplier effect at work due to fractional reserve banking:
http://figures.boundless.com/21073/f...quirements.gif
So while I get what you mean about digital currency having a psychological effect on consumption and savings, the fact is that the US Dollar is already predominately a digital currency.