Hmm, let's test your thesis the really simple way
Dollars/Euros/Rand in a rational market would cost only as much as they cost to make with perhaps a small premium.
Lesson: A medium of exchange (aka currency) is NOT necessarily a commodity.
Scarcity of the commodity vs. demand for the commodity drives the market price up or down in a rational market. I wonder if increased competition will do that to this market as more and more way to mine get distributed. I doubt it though, but time will pop the bubble anyway.
Lesson: I produce very few boogers, so they are scarce, BUT, importantly, there is to my knowledge zero demand for my boogers, so they have no value whatsoever. The number of bitcoins that will ever exist is finite (21,000,000), if the demand for them goes up, so will their price (or "value" if you wish to call it that).