If you're calculating it by comparing the prices of hardware you're not coming up with the real value but the lowest possible value that keeps miners mining. Why would the lowest value be the "real" value? You don't measure the real value of a car by the cost of parts and labor needed to make it. If we did that a lamborghini would be worth $50,000 instead of 500,000.
Yeah how could be the value of bitcoin to be evaluated? I am also confused to this and I have seen your post agreeing to it that the real value does not compromises on the hardware of bitcoin. However, my idea of evaluating bitcoin value is all about the supply and demand for it. The more demand from users for bitcoin the more its market price will be expensive.