Do view my thread on the theory whether BC are a pyramid-ponzi or not.
But the USD is certainly not. It is constantly printed and is directly correlating in the best case scenario to increase in economic output.
BC mining is not remotely correlating to any real world event and are mined out of thin air.
But if this service becomes the "only viable" service in its market say by gaining monopoly status (60% market share) in the anon-currency world and maintaining it then as a service it can be valued at this price or even higher.
That's the only question. Those investing in a "deflationary currency" are greedy individuals (we all got it a bit) trying to make money out of no produce and are thus contributing to a bubble which the actual users do not want.
Frankly all you folk into this and gold and silver and so on aren't doing anyone any good.
You're basically storing up funds instead of investing them back into the economy more or less hoping that everything else goes to hell.
You're hurting america
The difference is that since BC depends on commerce things aren't quite the same.
USD is printed without any effort, so essentially it worth nothing when the gold backing has been removed since 1971. Before, you can always exchange USD for gold at central bank so it has value. This is a critical point that most people do not understand or don't know
Since then, the value of USD is purely decided by people's consensus (like: if everyone believe it worth a cup of milk, then it worth a cup of milk), this also showed how a consensus can hold value for something for decades, even the fundamental support of value is removed
But the biggest question is: If that USD cost nothing to produce, how come central bank could use that nothing to buy something that has real value

This against any trading/bartering principle in the world. Again, the consensus (people's trust) are utilized by central bank
BTC on the other hand, is created by using modern processor and electricity, and that cost basically decided its base value, so each BTC worth something from the beginning. This is a fundamental difference
It's just BTC is new and people have not reached a consensus about how much a BTC should worth, it takes time to do this price discovery
In some people's opinion, you should totally forget about fiat scam and start to trade real goods and services for bitcoin, in this way you give it a value
BTW, it is not always a good thing to invest, all the investing is just a waste of resource when effective demand is low