Too many factors coming into play and too much subjectivity.
The real value of a domain is what an end user is willing to pay, depending on their motivation, financial means and negotiation skills...
I find that one of the ways to gauge value is to look at the market and research comparable sales.
Domains are not like real estate or commodities - due to their unique nature appraising them is tricky. In some way it is like speculating on the true value of Mona Lisa. How much is it worth according to you, if it were for sale ? There is no single answer to that.
Last year I sold a domain for 6K. After some back and forth negotiation the end user ordered 2 appraisals from different sources (I don't know which ones) and came back with two different figures: one in the 1$$$ range and the second one at around $2.5K. I stuck to my guns and they eventually paid my asking price. I couldn't care with their appraisals, I don't even know how they were computed. Note that appraisals are a double-edged sword: they can be used against you to bring down the asking price.
The important thing is not how much the end user is going to pay, but how much the domain can yield with adequate development. If it has the potential to take their business to the next level, then it is worth some good money.