It depends how you define "value". Is it only by price? A Ferrari is worth a lot of money, but it's also desirable because of what it is: something beautiful, fast and sexy. It's true that one BTC is worth more than one US$ but I think that as of today, the US$ is more desirable because it can be exchanged with many more people, in many countries, and without an Internet connection.
I like your statement we can't define the value by a price, there are a many factors will need to consider to defined the value. like the bold sentences it's means US $ is having more value than bitcoin because they are more needed by a lot of people. it's will be a different value for the US $.