OF ALL THE SILLIEST, COCKED-UP IDEAS TO FIX A CRANKY MAC, THIS TAKES THE CAKE. I couldn't, despite multiple restarts, get the search window in Launchpad (my preferred app launcher) on the MacBook Air to respond. No problems with the action on the MacBook Pro. Wanna know what the cure is? Log out of the user account then log back in.
Yep, as simple as that.