Can anyone shed any light on why most Previa's don't have the rear spoiler ? I only see a few from time to time with the rear wing. Was it an expensive option ?

The rear spoiler was standard on the Previas with dual sunroofs. Some won't have them because they've been removed or the rear hatch has been replaced without the spoiler. I've also seen a few with the spoiler that don't have the sunroofs. Generally, those were ordered as aftermarket items but most with the spoiler will have the dual sunroofs.