As someone else said, this has a great deal to do with market cap. While gold certainly has SOME value in electronics manufacturing or for jewelry, the price of it has very little to do with these things. It has a great deal instead to do with speculation. The price of gold would likely be only a fraction of what it is without said speculation and as such, ultimately is subject to the same inflationary pressures as other commodities.
In this way, the value of gold as an investment instrument has very much to do with speculation and not at all with consumption. Similarly, if BTC are seen to have value as a relatively liquid, semi-untraceable currency... it could achieve the same perception. Similarly, BTC as a transaction medium will become a sort of consumptive good as well. So to some degree consumption will drive price moderately (as with gold), but maintain its value primarily on speculation (as with gold).
The reality is that BTC has a substantial value as a medium for transaction. It will grow as does the technology to utilize it easily. It will also grow with a greater market cap and relative stability.
I think deriding its long term prospects because of volatility and such ignores that other commodities depend on like factors and mostly social psychology grants them their value.