Stop sharing primary [boot] and Time Machine drive via AFP?
Issuing the following command and restarting /usr/sbin/AppleFileServer would seem to have been the solution.

$ sudo /usr/bin/defaults write /Library/Preferences/com.apple.AppleFileServer admin31GetsSp -boolean true


It wasn't.  Connecting to the file server as an admin user continued to result in my seeing both share points and volumes.  I wanted to see share points but not volumes.

Issuing the following command and restarting AppleFileServer was the solution.

$ sudo /usr/bin/defaults write /Library/Preferences/com.apple.AppleFileServer fullServerMode -boolean true