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Awesome post. To throw one step further. I would like to propose the other site of your dark coin. Links that appear to exist but really have no value. This is common in the tactics of spammers picking up dropped domains and pitching them as high PR sites for link building. They have the signals of a strong domain, but futher evaluation proves that it takes more than strong moz rank to actually provide value to a site. I would assume the SEOmoz guys would say that the value is built in to their equation but you also have to remember that SEOmoz's linkscape only indexes a fraction of the web thats out their. It performs better in some niches than other. I find it useful to benchmark against a secondary source. I commonly check a domains metrics against SEOmoz and Majestic. Both have their own strengths. If I am link buying, I stay away from any site that doesn't perform well in both metrics as you will find that most sites with decent rankings do. This will save you from dealing with "made for link sales based on PR rank" type sites that have little real world value.

I was only looking at the source code on the Conversion Optimization page and not the home page. Face Palm