Yes, I agree with you that a portion of the value assigned to virtual currencies ( the IS value ) comes from the utility of the the thing... just like a portion of the value we assign to the U.S. Dollar comes from the utility ( you can carry it in your pocket and exchange it for stuff )... but understand that just like the dollar, we assign value to it because it's HARD to counterfeit ( and only because so ), you can't just make as many as you want easily.

Bitcoin, and most other virtual currencies, are only "hard" to counterfeit because limitations in current technologies ( math included ) make it so... What happens when that goes away?

What would the value of bitcoin be tomorrow if some scientist today, publishes a paper providing an easier way to factor large numbers? What about Moore's law? What about quantum computing and machine learning? What about breakthroughs in mathematics or cryptography? Start thinking about all the intellectual manpower working every day on any number of things that could make the very basis for bitcoin obsolete, and you start thinking that maybe the value we assign it is a bad bet.

As far as gold goes, until someone creates a philosopher's stone, or starts 3d printing gold atoms, I think we're safe to assume you would still have to mine the stuff and refine it, and that amount of work isn't going away anytime soon... and therefore the "value" of it isn't going to zero soon either.