The value is also based on scarcity, the difficulty to obtain (mine) it, the demand...
There are a lot of factors to be counted in, hence most use TA and extrapolation.

Also keep in mind that there's also another way to read those speculations on the price made by various people:
* some say it to show their support for Bitcoin (especially people involved in bitcoin related businesses)
* some say that so people will talk about... them