Ok, nice rendering, thank you!
One small thing, which to me is a big thing, but-
If you look at the illustration from the owner's manual, where it shows the back end of the car, and,
Look at the relationship between the height of the valances' horizontal bottom edge, and the lowest point of the vertical rear fender edge. In the GM illustration, the valance bottom edge comes down about two-thirds the height of the vertical edge of the rear fender.
In this rendering, the valance looks to be about half the height of the vertical fender edge.
Not a big difference I think, to most folks. but to me, that vertical fender edge is a bit too much like traditional Cadillac tailights, you know, those big vertical ones, and the huge open gap between this long vertical edge, and the area of the exhaust pipes, leaves this big gaping chasm. (I am aware this generates downforce) To me, that chasm looks odd, kind of awkward. It actually makes the rear fender edges all the more prevalent, makes them stick out like a bump on a log. They hang down kind of lonely, with no apparent relationship to the rest of the rear end. Drawing your eye to them, brings this fact front and center in your perception, which exacerbates their awkwardness. (to me)
So in GMs' manual illustration, this "chasm" isn't as pronounced. It's a bit smaller, and to me, this makes the rear end look more acceptable. To me, the rear fender edges look more integrated into the rear end as a whole, minimizing their long vertical "Cadillac-iness". There's a new word, right there!
The higher the valance, the more those fender edges contrast with the car, hanging down like turkey neck jowls. They either need to make the fender edges higher, or keep the valance edge lower, to avoid this old-lady, sagging-fatty triceps look.
I know, a very small difference to be sure, and not one that most people would sneeze at. I'm reluctant to even mention it. It's kind of funny, when you listen to peoples' objections to some aspect of the car that they don't like, and when you look at it, and you're reading their slant on it, you're like "What the hell is this guys' problem, he's straining at a gnat", where to you it's no big deal, but something else entirely ticks you off. That's what I feel, reading the objections of some guys. There are so many people, each with varying tastes, it's amazing GM could even design a car that can sell at all. Well, everyone has their little differences of opinion, or pet things that they like or don't like. I've heard people say they hate the headlights, I love the headlights. Some say they don't like the tailights, but I think they look cool. (Go figure, right?)
But that big gap between the bottom tip of the rear fender edges, and the exhaust pipes, well, that's a HUGE issue right there! (/satire)