While I like Plexus, and use it regularly for cleaning some headlights, I have never found it to be particularly effective as a scratch remover. I thought it used to be labeled as a cleaner/polish (I would have to check to see if I have any older cans), but in the product description is clearly states its current intended function...cleaner.
Have you tried Meg's PlastX? At least for my situation is is far more effective than Plexus as a scratch remover.