Patrick Walsh, who writes the blog, ManIA posted an article that is worth reading on an approach for measuring the value of intranet pages called "Content Value Analysis" This approach allows benchmarking of sites for parts of sites against each other:
"Each page would be examined and scored for its value against a set of heuristics e.g. if content is obsolete, outside of a review date, incorrect, incomplete or irrelevant the score would be 0. If there is some value on the page it could be marked as 0.5 and if the page content generally has value the score would be 1."
The objective is to provide intranet managers with a tool to assess the value of the portal or intranet that they manage. The page or section scores can be displayed graphically and can be used to motivate people to keep their sites up to date.