All currencies have exchange rate volatility. When Nano is widely adopted and denominated, its volatility will not be noticeable. Its price will be more stable as it will be driven by usage as opposed to entirely driven by speculation and its network effects growth will have leveled off.
Nano's value is driven by two things: the use of the payment system today and speculation on future use.
At this moment, its value, measured in market cap, is relatively low and almost entirely driven by speculation. If adopted and used as money, the value will inevitably be much higher and driven by use as opposed to pure speculation, similar to currency markets today.
As it approaches wide adoption, the rate of growth will begin to slow down and it will start to behave more as a store of value than an investment. In other words, it will preserve purchasing power, not necessarily increase it. Once its network effects are sufficiently large enough and have leveled off, Nano will behave entirely as a store of value used as digital money.