Our son was also obsessed with the Cars characters. It was the second movie that he had ever seen. He was about 21/2 and already loved anything on wheels. We stopped all tv and videos at about age 9 mos, when we read that the American Academy of Pediatrics recommends none until age 2 and then limited viewing at most. They are questioning the effect of quickly moving screen images on developing brains, their correlation to the increasing numbers of children with attention problems, etc.
We quickly found out how powerful tv/video and it's related marketing can be when we let down our guard and took him to see Cars at the theater. Disney and others know how to get into our children's brains. For many months afterwards, it was Lighting this and Doc that. Of course, the rest of his classmates reinforced it. We quietly stopped allowing new Cars things into the house, we stopped talking about it with him, and changed the subject. We also started replacing the Cars stuff with other better toys that encouraged creativity and movement...no bells, whistles, etc....blocks, simple trucks, cars, etc with no commercial attachment. We also stopped worrying about his learning curve, because we found out that he easily learned what he needed to when the time was right. I believe that the toy companies are selling us lots of stuff that our kids don't need by playing on our fears that our kids might get "behind". Check out the book "Einstein Didn't Use Flash Cards". We are culturally taught to push learning on our kids before they have the capacity to understand the lessons.
I know my views are not mainstream, but we've had great success with the path we've chosen. Our 41/2 year old's teacher is thrilled with his development. He's a very grounded, creative, gentle, smart, easy-going boy. Good luck!