A divisible and fungible asset like a currency can never be "too valuable to spend", since by definition you get the value of the amount you spend.
Of course it can. Lots of people here would not sell bitcoins at the current exchange rate because they think it's too low, so why would they spend them for something using the exchange price as reference? Unless they have no fiat currency it would be irrational, because converting fiat to bitcoins has a fee. It's more economical to use the fiat.
There will always be some people who believe that the market is underestimating or overestimating the future value of something. The people who will not sell bitcoins at the current exchange rate believe that the market is drastically underpricing the future value of bitcoins. There are also people who think that bitcoins will become worthless any day, and therefore you shouldn't pay $15 for them today because they might crash before you can do anything with them. These people think the market is overpricing the future value.
The exchange rate for bitcoins is the weird balance largely between these two extremes. This is, I think, a temporary issue for bitcoins. Either bitcoins will die or the volume will increase to the rate that people's disagreement over the future value is not so great.