From a practicality perspective: Most of the things that people want to retro-bright are either well over twenty years old, from a few different periods in Apple's history where some arguably poor choices were being made about the formulation of plastics anyway, or they're trying to do it because the machine and its plastics were intentionally put into a damaging situation, such as a smoker's home or sitting in direct sunlight, which I believe Apple has warned against since the very beginning. (That is often not easy to control, so I dont' want to make this sound like a judgement on the previous owner.)
From a personal perspective: I don't honestly dislike a Mac or an Apple II with a tinge of yellow, which is really what is happening in most of the cases when people retrobright things. It turns yellow again, or the case texture is lost, or the application process was arduous and difficult and somebody got it wrong, whatever.
So, I just try to match things up, or I just try to enjoy using these things for their nostalgic properties, and not worry too much about making them look new. In a lot of situations, especially with earlier Pluses and original Macs and a lot of the Apple II family, these computers were, for all intents and purposes, a color today we'd call yellow, out of the box. What most people refer to as beige is actually a platinum color, even on Windows PCs, and Apple systems that are beige get retrobrighted until they're either platinum or worse: white.
It's a personal preference, but I have seen "beige" G3s and the like when they were new, and while I"d prefer them in their original color, I don't personally believe that anything I can do is really going to accurately get that.
With something rare and itself more brittle and unreliable than usual, like an AppleVision or an AudioVision display, I'd be even more worried about retrobrighting it or making the (evidently, as in this thread) already bad plastics worse.
