Personally it seems quite a lot for a fairly untested currency.
US gold reserves currently worth something like $300Bn, the largest in the world (though it's no clear if anyones checked its there). All this is less than a company like Google but still $70Bn is a lot of money.
For the bitcoin price to rise a lot of money would have to flow in. Right now it seems like every grandma and her dog is being persuaded onto the bitcoin bandwagon. Is this not a sign of an impending crash, in which those at the bottom of the pyramid get burned? Is the bitcoin rise sustainable? Where will the money be flowing in from? Will shops have to start selling bitcoin investment scratch cards over the counter to keep the price rising?
I'm keen to head from people who can make arguments based on fundamental economic principles, either way.
Well the theoretical limit is the amount of wealth everywhere but bitcoin in the world, which is tons of trillions, so yes, Bitcoin is a tiny dot in a sea of potential wealth that can come in in various forms, be precious metals like gold and silver, stocks, bonds, commodities and all kinds of assets. BTC could be worth millions of dollars if people diversified small %'s of each of their holdings on their portfolios into BTC.
This should explain it better than any words (just consider BTC is not 70 billion and not 5, but like you see, it's still nothing, we are early adopters)
https://i2.wp.com/money.visualcapitalist.com/wp-content/uploads/2015/12/all-the-worlds-money-and-markets-dv.png?w=1360
This is a good vis. Makes it clear how small BTC still is and how crazy economics is.
Unlike the number of dollars in circulation, or the number of bitcoins in existence, the actual marketcap of bit coin is not 'real' in the same sense. The price of BTC in dollars can fluctuate arbitrarily based on supply and demand, this could make the market cap of BTC expand or contract by billions, yet no new money was created or necessarily even changed hands.