And answering my own questions ...
1) Places comes back when cinnamon is restarted (either log out or alt+f2 & type 'r').
2) To edit the 'preferences' and 'administration' submenus you have to edit the *.desktop files found in /usr/share/applications/ those with Categories=Settings; appear in preferences, those with Categories=System;Settings; appear in both. To avoid entries appearing in both you can edit /etc/xdg/menus/cinnamon-settings.menu and remove the <Category>Settings</Category> entry from the 'Administration' menu - e.g.
- Code: Select all
<!-- System Settings -->
</Menu> <!-- End System Settings -->
Then edit the appropriate *.desktop files to make sure they go where they should!
Hopefully someone will eventually integrate this functionality into the cinnamon menu editor.