The title of this thread relates to the abductor and Jane Tanner.
I believe that the Smith sighting is far more significant insofar as it relates to the question of an accomplice than Jane Tanner's.
It is from the Smith sighting - a more reliable sighting in any case, being one of several people, walking in very close proximity to the abductor - not Jane's, that we can infer that the abductor must have been covering a significant amount of ground on foot.
It is near implausible that a person of sound mind would have been planning to walk around the town with an abducted child around the time of the child's discovery. From this, we can go two ways. We can reason that the abductor was indeed not of sound mind, a disturbed individual with the oft-accompanying diminished sense of self-preservation, whose plan had never included a car. Or, we could infer that there was supposed to be a car, but something went wrong, a scenario which probably - though not necessarily - would have involved an assistant. How else can we explain that sighting?
I do not agree with all the conclusions in Sadie's theory and how she reaches them, but the fact remains that, thanks to the Smith sighting, we have plenty room to argue a driver's presence by implication.