Bitcoin as a currency is being inflated, currently, at a rate of 28% per year. That alone would disqualify it as being one of the "hard" currencies (i.e., United States dollar, Euro, Swiss franc, British pound sterling, Japanese yen) for a long time to come.
Bitcoin most definitely is driven by sentiment and with the aggregate of all order books being slim, it can likely be manipulated up or down with simply a six figure budget.
Where bitcoin's primary advantage comes into play is that the currency inflation rate a year out, two years out and ten years out is already known, today.
Additionally, when trading currency there is no T+2 settlement. Most Bitcoin exchanges settle trades instantly, and deliver bitcoin withdrawals in seconds. Thus the funds can then be used for spending or further transfer just minutes after the trade executes.
Unfortunately, the bitcoin exchanges are not as great with the flow of fiat used for trading. Arbitrage would keep the exchange rates about even (less trading costs) however because fiat funds don't flow cheaply or quickly in and out of the Bitcoin exchanges, exchange rates between exchanges will not be consistent.
This presents an opportunity to some, but serves as a hurdle to others. Because bitcoins are not traded yet alongside other currencies for forex or are yet considered by established financial trading firms, there are first-mover advantages being enjoyed by entrepreneurial endeavors writing custom trading bots.
One other benefit is that Bitcoin is just a protocol and data, which means it is universal. Central banks don't need foreign exchange reserves with bitcoin nor swap agreements to trade against bitcoin. There is simply self-interested individuals and companies doing the buying and selling (for both commerce and speculation).
Here are some other benefits: