When the Inspector sidebar is not visible, pressing either Cmd-3 or Cmd-4 (the hotkeys assigned to switching between them) will activate the sidebar, and switch (if necessary) to the respective panel. Optionally, pressing either hotkey when that view is already active, will dismiss the Inspector.
Hmm, that is difficult because the shortcuts are actually created by the menu. So when the menu isn’t visible (ie. when the inspector isn’t visible), the shortcuts aren’t available. Given that this is very, very, very minor and you already have keyboard shortcuts for toggling the inspector, I am going to take a very long raincheck on this one. 