How could one make an automator script to restore all hidden windows quickly?
This AppleScript should restore all hidden windows.

The first action unhides any hidden programs. The second action restarts the Dock, which has the effect of un-minimizing any windows minimized to the Dock.

tell application "System Events"
    set the visible of every process to true
    do shell script "killall -HUP Dock"
end tell


If you particularly want an Automator workflow, give it one action: Run AppleScript, and assign this AppleScript.