Re your comment about currency production costs: A spike in electricity costs would directly effect existing bitcoins' value. A spike in cloth paper prices would not cause a meaningful change in the value of already-printed dollars. And the price of the dollar would spike with electricity costs indirectly. They're not the same, it's an invalid comparison that neatly evades their inherent technological and conceptual differences.
"Store of exchange-value" != currency, and BTC is currently behaving best in that role. Admirably, really- see how it's spreading like hotcakes in China. That's as a store of exchange value, not a currency.
You can't turn your gold "back into" ore or your diamonds "back into" carbon. The cost of an airline ticket is mostly determined by the current price of fuel.
When BTC starts to be used as a currency in earnest we can revisit the issue. Although at that point, you will be able to exchange your BTC back into electricity or other commodities through speculation or arbitrage. Which you can actually do directly right now if you know the right people, anyway. Profitably.