I think you did a great job with the wing. Looking at the way it's attached (and given the thing itself is an "exact" replica), I bet it actually does some real work at track speeds (thinking stability in very high speed sweepers and stand-on-it breaking situations at the end of long straight, heading into a slow-speed sequence). It looks a lot like the wing on one of the Team O'Neill rally cars.
A couple images of that application:
So, so me, this wing is more functional than cosmetic (hah, rare to be able to say that) which makes me wonder about the lip/splitter. Is there any under tray to that thing or is it like the Triple R piece -- purely cosmetic? I'd be wary myself of adding downforce to the back end without something on the nose to help balance/tune the aero effects.
Thanks for sharing. I think that wing is a good option (with your attachment setup) for someone wanting to tune out any rear-end instability.
My opinion: It's not really just a spoiler as it actually sits in the relatively clean air stream just above the tail of the car, and assuming it's "flying upside down," the wing provides real downforce at speed -- not so much for a daily driver. A spoiler is usually just a device that is flush to the hood (or maybe with a bit of a vertical lip) meant to break up the trailing edge vortex (reducing drag and lift).