1. Is the spoiler urethane or fiberglass?
It is same kind of non-glass flexible material
2. Does it tend to seek out parking curbs and other obstructions on it's own? I had a car with a front air dam that was pretty battered from parking curbs, but I was also younger and dumber at the time.
Some people think there is some kind of law that the tires must touch the curb when they park. The spoiler won't seek them out but you have to use a little common sense, esp. if you lower the car.
3. Does it act as a snowplow in winter weather...i.e. will it get stuck where otherwise it might have made it through the 6-8 inches of snow?
Never been a problem for me in South Florida
4. How does it mount? Does the old valence remain or does it come off?
Old valance stays in place, mount using all oem hardware
5. Can anyone use the magic of photoshop to make a Arctic Blue 535iS 3/4 frontal shot? I can't quite visualize it in my mind's eye.
Can't help you on that

Thanks in Advance,

Brandon