While I imagine some might find it useful for users to know the technical name of the pieces of their operating system, most will only know wingpanel as the menu-bar, plank as the dock, and slingshot as the applications-menu. I recommend using the common name as their primary names, with the technical names as aliases and mentions in the tag usage recommendations. The duplicate pantheon-dock should also redirect to the existing tag.
Most of these tags simply aren't in use, and typically we encourage the use of tags being the exposed name in the OS. For wingpanel and slingshot that differs a little, but
file-manager goes to
greeter. I have added the wingpanel and slingshot redirects in a similar style.