I think, when you are editing a gallery you can choose "preview" from the "Show Visitor View" drop down menu.
Anyway what I often do is I edit the gallery in a Firefox window and open a second window for viewing the gallery. When I want to view the gallery while logged in I open the second window in Firefox. If I want to see the real visitor view while not logged in I open the gallery in IE, where I'm not logged in. After I've done some edits simple press the refresh button on the browser window showing the gallery view.