There are two possibilities that might work for you.
First is the Book feature. A documetn can be added to as amny books as you like, but you risk changing page numbers, or sytles and master pages, if you synch.
The other possibility is to place the pages from the "master" document into another document as links. Edit the master, and aywhere it's linked you can update. You cannot edit the linked versions directly in the new files. There's a great script for placing multiple pages, too: InDesignSecrets » Blog Archive » Zanelli Releases MultiPageImporter for Importing both PDF and INDD Files
Wow! You're good! Couldn't find info. anywhere. Thanks for your help!
We like to think this is the best source on the planet for information about InDesign.