think you will find with plastic/rubber trim unless it has been loving care from the word go it may take a while to get it back to its former glory.
i have found though trying to revive our trim it did not happen with the first few treatments bur after a few months it starts to come back
.
the same goes for the interior trim.found it very patchy for the first few applications but over the year we have owned the zed the trim has come back to some of its former glory
just what i have found doing ours.
and yes i have used meguiers ultimate protectant dash and trim restorer