Very nice! I have this project ahead of me before winter hits.
I tryed the product called Bondo Restore Black. I had to tape off the molding on the doors, and apply about 10 coats. It wasn't perfect but looked good. It is fading after two months, the box claims 6 months before need to re-apply.
I am thinking of a really good de-grease, and then some krylon fusion or whatever that bonds to plastics, and then a UV resistant clear coat. Would give a long lasting, dark look, but would be a PITA to touch up.
Anyways this is one of the best, cheapest and easiest ways to make our Xjs look better.