I am not claiming that a potato will not be worth as much as the highest bidder is willing to pay for it. I am instead claiming that the price of a potato will always return to value determined by its utility.
Just like the gold's value returned to the utility-only value? Just like Chateau d'Yquem ($50k/bottle) is now worth same as any other wine sold at supermarket? Just like you can now buy white truffles at $1/kg?
Price is determined by supply and demand. Scarcity is a factor that drives the price up - whether you want to accept it or not. Utility itself won't automatically create monetary value, for the same reason you won't pay for air, even know it has huge utility - it keeps you alive.