$320 is only the equivelent of
200k people investing $19,200 ever in their life so far (on average)
600k people investing $6,400 ever in their life so far (on average)
2mill people investing $1920 ever in their life so far (on average)
now imagine there being 7 billion people in the world and only 1% of the world ever put 1 months salary (about $1920) EVER into bitcoin
70million people when all coins are mined.. each coin is worth $6400, or currently with 12 mill coins mined. each coin is worth $11,200
so there you go.. theres some possibilities of population uptake and average financial input figures, to get your minds playing about with
The problem with your calculations is that not even the US Dollar, which is the most widely used currency in the world, is used by 7 billion people for purchases.
And your assumption on the average monthly salary is pretty extreme for the majority of the population of the world.
I do believe that widespread use of bitcoin will drive it up in value, but I'm questioning your calculations, and assumptions used in your calculations.
Another point is that it takes technology to use bitcoin, even if its only a cell phone, it has to be a smart phone. The cost of smartphone plans is not affordable to a huge portion of the population in many countries.
I hope to see a low tech solution which will allow trading of bitcoins without the overhead required now. That will boost the use and acceptance of bitcoin and increase its value significantly.