Libraries can weight their own formulas depending upon the importance of these activities to them. Citation figures are available to us through ISI's database. Use by readers each library has to count for itself. Not many libraries are organized in such a way that they can count uses of periodicals. That is the first thing libraries must change.
Libraries spend too much money on serials to have so little knowledge of how they are used.
It is simply a management problem. I propose that libraries should, with public discussion, and the approval of faculty and university administrators, decide what percentage of the materials budget will be devoted to the purchase of locally-owned journals. If the percentage of funds devoted to subscriptions climbs above the agreed on figure, that is an automatic trigger for cancellations. It might require a consortium of libraries to define use and perhaps to purchase ISI citation information in the form useful to each library. With these moves, libraries would have the tools by which to respond immediately to budget cuts or subscription increases.