Putting side the utility of gold (e.g., tooth fillings) and diamonds (e.g., cutting devices), art is fuel for the soul. Gold and diamonds are used to create objects that gives you motivation to do more. You enjoy art (and music) as an end to itself and not just as a means to an end. This idea of things being consumed as an end in itself applies to many things. Take for example a piece of steak. You can eat any cooked piece of meat to get protein for you body (means to an end). Yet you are willing to work more to get more money to spend on a nice piece of steak in a romantic restaurant. This is an example of fuel for the soul. Man is not just an animal. He is an animal with a *volitional* consciousness. The fuel is to give his violation to do more.
The same reasoning can easily be applied to bitcoin too, since for some people acquiring bitcoin is an end to itself and not the means to an end,such as to gain wealth in the future. People may enjoy this feeling of being able to control their money through cryptographic keys, or they may like the fact that their share in the total supply of money either stays the same or increases, that it cannot be diluted and taken away by powerful corporations.
I disagree. There is the objective theory of value. That is, that which is valuable to your life is substantiated by objective fact. Take for example water. Water, in certain quantities, is objectively valuable to your life. You can pretend that it's not all you want, but you will be dead after a certain amount of time if you do not consume something that has water in it. This is an objective fact not subject to any subjective whim.
Things without which humans can't live are, by definition, objectively valuable. But they remain objectively valuable as long as in abundance. Once these objectively valuable things become scarce, humans start to value them subjectively, basing their reasoning on current circumstances. For example, water in the desert is valued more than that in places near rivers with fresh water. The objective value of water always remains the same - it helps you quench your thirst - but the subjective value fluctuates considerably.