Value of Libraries - SIRSI report on Value of Canadian Libraries: Impact, Normative Data, and Influencing Funders http://www.sirsi.com/Pdfs/Company/Abram/StephenAbram_ValueCanadianLibraries.pdf
This report has information that stretches across North America. Check out the references for links to recent studies on value of libraries from Florida, South Carolina, as well as school, academic, and special libraries.