Economics defines value as that which a rational agent is willing to make a sacrifice for, and the degree to which something is valued by that actor is exactly measured by what they're willing to sacrifice.
Why is this not valuable? Or, rather, what might a better definition entail? A precise formulation isn't required, I'd be happy to see a rough sketch of necessary and/or sufficient conditions.
Particularly, I think it's important to delineate whether 'rationality' allows for arbitrary actions, decisions, and desires. I do include these qualities in my notion of rationality, so long as the actor can rationalize the phenomena to themselves (even if this rationalization is based on nothing more than their ability to do so).
Given this notion of value and rationality, yes: I can very easily allow for NFTs ('useless' though they are) having value.
Do you mean 'rational' in terms of 'every action or desire is reducible to some unknown deductive logic'? In which case, I agree that everyone is somewhat irrational and furthermore that nobody could ever be rational. 'Rational' in the game theory sense? In which case, I see no reason to say that everyone is irrational instead of allowing for the mathematical notion imperfectly capturing reality.
It is possible NFTs do have value in the sense of being good, but them being priced highly does not give us useful signal there.
I suppose my biggest gripe is this: how do you construct a notion of rationality which allows for some people to be perfectly rational sometimes, imperfectly rational at other times, and others to be rational never, while allowing for real flaws in reasoning and the absence of perfect information? (this is, to me, a rough sketch of some necessary/sufficient conditions)
And, again, the notion that something is 'clearly false' at some point presupposes perfect information about the context within which the belief is held.