Looking at that close up of the Well Walker and the pop number, I'm surprised Stern didn't simply put the well walker on top of the pop bumper.  Not since the 1970s has there been a reason for anyone to shoot for a pop bumper.  Up until the 1970s, a single hit on a number 'when lit' earned a substantial number of points.

May not have worked to well here, in regards to scoring rules, with the bumper being part of a set of three.  But a bash toy on a bumper is something I'd love to have seen.  Then again I am likely not speaking for the majority - I love randomness in games which is contrary to most players who want every successful shot returning the ball to the flippers.