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.
I don't think so. The most common way for people to value bitcoin right now is that bitcoin is treated as an asset and not as a currency itself. I believe that around 90% of bitcoin holder right now are either using bitcoin for trading or simply holding it, or they would convert it first into fiat before using the fiat currency for buying stuff. Either way, bitcoins are not used as a currency but as an asset.