-D—Do not delete the directory before unpacking.
-a 1—Unpack the archive specified by the source1 tag after changing directories.

Finally, two additions to the %files lists were required, one for the client:

%doc amanda-client.README

and one for the server:

%doc amanda-server.README

At this point, the packages are complete. Certainly there is software out there that doesn't require this level of effort to package. Just as certainly there is software that is much more of a challenge.