A lot of how much of the sidewall gets used depends on a couple things:
1. How low the profile of the tire is
2. How much running tire pressure is present.
I have 235/40-18s on my car, and at around 38psi the sidewalls don't flex enough to be used in cornering. . . even in autocross.
For the shine, I use Meguire's gel . . . it goes on clean with an applicator (none on treads) and stays on through a few washings or a couple weeks of intermittent showers. From what I've gathered, it's one of the safer ones to use, too.
Hell, I go through tires fast enough as it is, though. . . worrying about sidewall welfare isn't something I trouble myself with. . . .more like treadwear from the mileage I rack-up and the abuse I dish-out at the track every few weeks.