Not sure I follow your logic as far as price-discovery. The mere fact that a coin is increasingly hard to mine does not make it more valuable. Market demand does. Now if you say difficulty reduces supply, you'd have a partial basis. But again, scarcity alone does not create value if it is not met with demand.
I don't entirely agree. The kind of "demand" you speak of is not entirely rational and market-based, nor necessarily sustainable. There is a large element of miner-speculation, and that could go south if the pay-off disappoints. Many are mining it just to follow the herd.
Totally with you as far as the useful role irrationality plays. Let's hope it goes bonkers completely, just as it did with bitcoin. Mind you, most of the people buying bitcoin did not treasure it for it's colossal level of mining difficulty, or even know what difficulty is or means. My point was only, there is not a simple logic going from how hard it is to mine something, to what it will be worth on the market. There are many factors at play simultaneously. I think miners can get a little delusional on this point, imagining that all the resources they pour into a coin does, or 'should' automatically make the product more precious to others.