I'm Buddhist, so I'm answering this question from my real-life standpoint:
Authentic Realization of one's Ultimate ( original awareness ) Nature.
What could be more precious?
Given that ALL of one's unconscious-mind's mechanisms exist to block that from happening, to protect unconsciousness's Eternal unbroken dominion, what could be more difficult to earn/obtain?
All the distractions in the world, "helping" one to NOT earn one's deepest profoundest Truth...
All the profits that cease, should one get anywhere in self-realization...
You simply don't need any external resource, for there to be a most-precious-resource, you know?
I was just about to post a question asking for suggestions for something I could use like this for my world, and of course I find this question from a week ago lol.
I might post it anyway just to revive the conversation in other, similar communities. It's a useful MacGuffin.