If "valuable" is defined by the users then it would be the content they refer to most often. I was surprised by some real world SharePoint usage stats I generated for one of my customers.

 

Although they have more than twice as many Word documents than Excel spreadsheets, the xls files represent 44% of access to existing files while .doc. only represented 10%. No other type was above 4%.

 

This customer has over 400 Gb of content in over 600 team sites running on 6 web apps with 12 content db's

 

16% of the sites get more than 100 visits per day and only 2% get less than 1 visit per day (on average).