The value of academic libraries is often strongly tied to the value of colleges and universities themselves.  There are many reports on the impact of universities and colleges and higher education on the economics of a community.

2005 Colorado Academic Library Impact Study (Feb. 2006)

Libraries Designed for Learning by Scott Bennett

Dimensions and Use of the Scholarly Information Environment

Pew Internet and American Life

OCLC White Paper on the Information Habits of College Students

OCLC Report: Research Libraries, Risk and Systemic Change (pdf: 579K/20 pp.)

First-ever National Study: Millions of People Rely on Library Computers for Employment, Health, and Education

Canadian University Library Benchmarks

ACRL and ARL

ACRL has a list if 8 studies here:

Value of Academic Research Libraries

The ARL Statistics and Assessment resources are here:

ARL Statistics

The ARL site covers some of the StatQual, ServQual, ClimtaeQual, DigiQual, and LibQual resources which are other metrics used in academic libraries to judge effectiveness, impact, and value.

In addition it is worthwhile reviewing some of the work in the following:

Evidence Based Library and Information Practice

Educause / CNI