Francois Druel has done an in-depth investigation on how to evaluate immaterial resources as to their ‘value’.
His PhD thesis on the topic is available here at http://homepage.mac.com/fdruel .
He uses “use two axes : attractivity and perennity. To determine each axis a total of 18 criteria are used. For establishing the weight of each criteria, I use a empirical methodology based on observation. The result is a “magic eye” diagram that can be read directly or used for comparing two projects.”