Since the domain name appraisal industry is so young, perhaps there are other industries that it can look to as a way forward. Domain names are often described as 'virtual real estate'. Real estate exists at a physical location, and there are likely to be many similar properties nearby, some of which will have recently changed hands. This makes real estate valuation a relatively easy task. Domain names are by their nature, unique, and any attempt to locate 'similar' names is laden with traps and pitfalls.
Real estate has a cost associated with building it, which gets built into the valuation figure.
They are intellectual property in its purest form. So it seems that any similarity between domain names and real estate is superficial at best. Domain names have objective 'physical' characteristics which can be used to help value them e.g. length, number of words, spelling, etc. With painting, the identity of the painter goes along way towards valuing the work. So there are some distinct similarities, but let's not fool ourselves, domain names are not paintings.