I think that the most common way to value Bitcoin is like valuing other currency by another currency.
Seeing to it that we all know all the factors that causes or affects supply and demand equilibrium.
Also the time we hold bitcoins. Time is very important factor.
For me the best thing to value Bitcoin is to save it for the future, but not save all we must use them also and try how it works. Bitcoin can be the future of finance as one of the expert says. Maybe bitcoin in the near future is being accepted by not only online store but also local store in different country.