Spencer has been getting pretty good at playing with his big car lately. It is clear that he is really close to walking, because he is not really relying on the car for balance. Occasionally he will stand up on his own when he wants to inspect something with both hands, but then once he realizes he is not holding onto something, he quickly finds something to hold onto, or simply drops to his knees. So I think he is ready to walk physically, but not quite there mentally yet.
In this video, he displays how he is now able to turn around and go the other way when he reaches an obstacle with the car. At the end, he switches over to his small Lightning McQueen car, which is actually filled with bubble bath.