How to keep showing Administration menu when changing user?
There is the Masquerade module for seeing how a page looks like for another user https://drupal.org/project/masquerade.

Another way is to duplicate your tab in incoqnito tab or in another browser and become another user there.

Third way is to make sure (if possible) your browser remembers user names and passwords on login forms. Then logging in as administrator is as easy as typing the first letter to the username field and pressing enter. This is less cool of course...