You are wrong for one reason. You assume that bitcoin's only use is for point of sale transactions. It serves many other purposes. Why bother with bank wires anymore? Or traditional banks for that matter?
Sure, bitcoin can be useful as a replacement for bank wire transfers. But after the transfer the reciever will probably sell the bitcoins on an exchange for a more well established currency, and so then the bitcoin market price would drop back to where it was before the sender bought the coins. That kind of use would not cause the market price to go up.
The reciever could keep the coins, but what for? Either hoarding (speculatin), or for actually using it as a currency.
A currency is used used as a way to pay for goods and services and to pay people for their work. We would see these transactions for goods and services in the blockchain, but we dont.
people store it. That is, it has value because people do not immediately liquidate units of A to get units of X. If no one wants to hold A, A has no value. People hold currency/gold/shells because they anticipate that it will have value in the future. Collectively, this gives something a global value. So, I reject the notion that value comes solely from ease of convertibility. Gold is a perfect example.