A couple of random thoughts...
If the governments crack down on the exits (exchangers), leaving no way to redeem BTC into a sovereign currency, then you'll see a crash back to single/low-double digits.
Not likely as there will always be a country that will do the exchange for a large cut, and provide the gateway for conversion into USD, EUR, CAD, CHF, AUD, JPY...
Have to remember, one of the key features of BTC is built-in scarcity. In the short-term, the price of BTC is currently mania-driven. In the long-term, it's based upon scarcity + the conversion premium into sovereign currencies...
If a full-fledged economy develops which eliminates the need for conversion, then scarcity will be the sole determinant of price. BTC per transaction will slow devolve towards 0 as the price of 1 BTC increases... And it will increase due to increasing demand and finite supply.
Most likely, some day down the road, it'll die off or remain a geek-thing because regular people hate decimals. Buying/selling something for .0025 BTC (and trying to figure out how many $, Euros, Yen it represents) will greatly annoy the masses...