Hi Dave

If your Master Document hasn't shown signs of corruption, I suspect it will
not be long before it does.

These articles may be interesting (if frightening) reading

Why Master Documents corrupt
http://word.mvps.org/FAQs/General/WhyMasterDocsCorrupt.htm

How to recover a Master Document
http://word.mvps.org/FAQs/General/RecoverMasterDocs.htm

I would recommend that you move away from master documents altogether and
use RD fields to create a consolidated TOC & index from your document set.
This article shows you how to manage this process. It has the advantage that
you can copy a document set to a new folder and everything will still work.

Creating a Table of Contents Spanning Multiple Documents
http://pubs.logicalexpressions.com/Pub0009/LPMArticle.asp?ID=148

I'm anxious to see other responses, because I'm trying to do something
very similar.  In the meanwhile, though, there are two suggestions I can
make:

First, depending on the content for what are now subdocuments, you might
be able to use autotext entries.  While they are generally menu-driven,
you could probably use radio button controls and VBA instead; that's out
of my expertise.

Second, the best way for you to do what you want is really with a
document assembly program.  HotDocs is the only one I'm familiar with,
and it works nicely with Word; there are others, too.

I'm late with this, so I hope you are still around, but an alternative to
the other suggestions might be IncludeText fields.  If you Insert | File,
but check the box "link to file" then the text of the inserted field is
added as an IncludeText field.  This is another way to create composite
documents--as you edit the inserted file, you can update the field in the
composite file to pick up the changes.

It might be particularly appropriate in your case, because if you created a
doc with a includetext fields for *all* the specifications, then toggled
field codes (alt-F9) so that all you see is the {INCLUDETEXT "name of file"}
code, it should be pretty easy to do a Save As, delete the unwanted fields,
then toggle field codes back and print, email.  Probably also a good idea,
for each project, to then Unlink the Fields (cntl-shift-F9) so that they
become text and you have an unchanging record of the specifications you
started each project with.

Ideally, you would create a template that includes all the fields, the TOC
field, and whatever other formatting, which would prevent you forgetting to
Save As.  

I think this would be pretty close to the ideal form you describe.