...and I'd rather win a gold medal than a silver, but it doesn't mean a silver isn't better than a bronze.
Reading Mac128's post, and trying to understand the spirit of what he's saying, I don't think he's advocating you *not* try to get a non-yellowed case, but more, the value of very yellowed cases (with serial numbers riveted or engraved) are low. I think we all want to protect pieces in good condition, and if finding new uses for poor examples makes them worth something to someone, well, better than the landfill.
This is no different than the debate among classic car collectors and hot-roders. The majority of the bell curve falls in the "don't fuck up nice examples of classic cars" and "feel free to hot-rod something with flaws" camps.