Marginal effects don't really reduce well to narrow examples like that.
What I mean is that if you assume a healthy trade in something of limited abundance, you should be prepared for demand to drive up the value of that thing. It might not, but given the simple dynamics of supply and demand (microeconomics isn't really controversial), it is prudent to be aware of the possibility.
(I do sort of assume that people are mostly using bitcoins to complete transactions and speculate, I don't assume there is a healthy trade in them)