I routinely use the same files in numerous books. These are technical manuals that often share the same common content. I just update the TOC and PDF the book. Since all share the same styles life is easier yet. The only problem I run into is on the larger manuals. I hit Indesign's limit for the number of files that can be open at once. This occurs when making the PDF. My books are up to 120 files with many placed ID files all running to about 500 pages.