I look at domain names based on a few criteria, some are technical and some relate to unspoken metrics... the feel of the name.
Like any real world appraisal it depends on how you are using the asset. A vacant low-lying piece of land surrounded by high ridges and lined in clay may be worthless as a residential real estate site, but priceless as a landfill. Similarly, the value of a domain name changes depending on whether you're building a media co on domain foundations, or whether you're in the business of selling the names themselves.
This topic deserves a more thorough future post.