At the end of the day we live in a world governed by supply and demand.
We're not going to shift to a 'usefulness' based mindset, and we should avoid shifting to the mindset that an object is equal to the sum of it's parts. Supply and Demand are king.
But demand for gold is not just jewelry and electronics. Demand for it as an alternative to fiat money is inversely proportional to peoples' trust in fiat money. So gold can be unneeded as an alternative for decades, and then be needed. Gold can be completely written off as a relic, a dinosaur... and then suddenly it's not.
In the case of gold, I think it is useful to look at the types of demand - jewelry and electronics consumption vs. currency hedge and speculation. In this way you can learn a lot about gold from bitcoin and vice versa.
