After 4.0.2 update, the Explorer View->Toolbars->Classic Explorer Bar is greyed out. I even rebooted (PITA) to see if that fixed it but it didn't.

Most likely the addon got disabled for some reason. It does not usually happen when you upgrade. Maybe you have some security setting that automatically disables addons after they are installed. To enable it again try the steps listed here.

The 'Classic Explorer Bar' also included the up button.