In my understanding, number of bitcoin users now is only 350,000, less than a million at least.
When it reaches 100 million, we are still in early adopter phase in global scale.
It is very important to realize that all growth has its limits, and the limit for bitcoin growth is that it replaces all other liquid wealth. That would lead the purchasing power to be in several million$ range. A more conservative scenario, that of replacing gold, would put the price at $300k/BTC.
The problem with your estimate is, is that you forget Bitcoin isn't the best coin.
The other altcoins like Feathercoin and Peercoin use less energy/need less miners/have 30times faster transaction times/have more coins/better in every category. Might take another year or two, but the coins with the most benefits will be the higher echelon coins, specifically not Bitcoin(unless someone completely changes everything about it to make it better in every way shape and form).
Bitcoin is only extremely more popular for it's capitalization on early mover and early promoter in the beginning. Other coins will easily be worth more.