There is some simple math that drives the whole valuation issue.  I evolves around assumptions of adoption.  Given the current real world obsession with mobile payments, more efficient payment mechanisms, and fiat currency devaluation it is a given that cryptocurrencies are inevitable.  It goes without saying that financial services infrastructure will be built to lever BTC's competitive characteristics with the current payments  system.  Add to that the the 3 major economies of the world are in a runaway financial disaster (USA, EU, and Japan) there is really no other option than devaluation.  Hence, BTC as a usable currency or a valuable investment.

So assuming some type of adoption rate (I believe 10% is a reasonable number) then you can easily factor a valuation of BTC to the USD (assuming world currencies generally remain at their current relative value).  Currently there are approximately $22 Trillion USD in various parts of the money supply.  At a 10% adoption rate of the USD alone (The global fiat currency money supply is north of $100 Trillion), BTC would be worth approximately $100,000.