I’ve found a dirty hack to hide the menu bar in Mavericks while the Quartz Composer viewer is in fullscreen on an external display:
1. Right click on Quartz Composer app -> show package contents
2. In the Contents folder, right click on Info.plist -> Open With/Other… and choose TextEdit.
3. At the end of the file, right before </dict> add the following:
It should look like in the image: