Patrick- Well, "familiar" is sorta relative, but I DO know what you're talking about. Had I detailed MY allroad (instead of getting rid of it) I would've used AIO topped with BFII or P UPP (or MAYBE SG) on *ALL* the trim in question (side trim included). When it comes to plastic trim on Audis, *I* always just treat it like it was painted. I've been doing this on VW's and Audis for a LONG time and I've never had a problem with it. It never dried out or otherwise seemed to suffer from my methods.
For me, using an ERV dressing or plastic polish would be a REAL hassle (keeping it off the paint, for instance, and getting it to look uniform) and wouldn't offer any advantages. And the first time the owner got caught in a storm or washed it, it would look crappy, whereas the "treated like paint" method would hold up fine.
Also, I dunno about using a plastic polish. If it's abrasive it might be a bad idea. Many of the black/gray Audi plastics are NOT colored all the way through (you learn this stuff when they get wrecked). I've used clay, AIO and Pinnacle PCL on them, but that's as aggressive as I'd like to get.
I recognize that 303, etc. have UV blockers and would "condition" the plastic/rubber/whatever, but it just wasn't an issue on any of my cars, and I had some of them for a LONG time.