...I tend to side with the OP as I feel I get more explanations for the viewpoints given.
"For every complex problem there is an answer that is clear, simple, and wrong."
--H. L. Mencken
I'd be glad to explain in greater detail anything you don't get, but I'm afraid there's no simple equation you can plug some variables into to get the value of a currency. Value is subjective, and each person will value a currency a different amount. The purchasing power/price of a currency is a result of these subjective valuations interacting.