IFLA has released Guidelines for Planning the Digitization of Rare Book and Manuscript Collections.
Here's an excerpt:
These guidelines attempt to complement this body of knowledge by addressing the specific needs related to planning digitization projects for rare and special collections. They are written from the point-of-view of special collection managers, rare book librarians, curators, and researchers who study the physical object as an artefact bearing intrinsic historical evidence as much as for the intellectual content that it contains.
Digital Scholarship | "A Quarter-Century as an Open Access Publisher"