IMHO it's not the right way to think of bitcoin in this fashion. Though I'm sure that 99.99% of BTC buyers/sellers nowadays are interested only in the value of BTC in FIAT currencies as they hope to exchange it back into FIAT when it will reach some "FIAT" value. But I believe it's just temporary hype and with wider adoption by merchants people will consider BTC a real currency and they will use it for buying stuff instead of trading it for some worthless FIAT currency which BTW will lose its value more and more in the future (for its nature). I think that selling BTC for FIAT is just waste of BTC.
The value of BTC is the stuff you can buy for it and how much do you value it for yourself. For most people that stuff is some bullcrap FIAT currency, but it will change, trust me

Think of BTC as buying power, and the exchange back to Fiat as a stop gap to expressing that buying power.
The real value is in store of value and large value transfer, eg in 10-100 millions if not billions at will.
This is something that Fiat nor the current banking system can offer, in any form. They buying of nick nacks from amazon/ebay or coffee is low value. Look at thier market caps, versus the value of the property market, high value.
This is to some extent why I think Peercoin may be the better solution.