After many, many years of buying $10 "cheap sunglasses" I finally decided to see if the people who said good glasses were worth it. Unfortunately, after dropping $[...] on a pair of Ray-Ban Aviators, only a year later, they got smashed in a bad bicycle accident. The fact that I ordered a new pair a few days later is a testament to how convinced I am that good sunglasses with glass lenses are worth it.
On the first day, a pair of Aviators don't feel significantly different from the $10 knock-offs. They aren't lighter, the image isn't clearer, the eye protection isn't better, they don't look better on me. But after just a few weeks of mild use, the cheap plastic-lens glasses start to get smudges and tiny scratches, almost too tiny to see. You don't notice it at first because it progresses so slowly and gradually, but little by little, the view through them gets muddled, they get harder to clean, and you start hating them, all without even realizing. One day you get new ones and the sudden contrast is striking -- wow, these are so much better! That's your only clue for how bad the old ones really had gotten by such slow stages you never noticed.
Glass-lens, good quality sunglasses are like that first day every day. They don't develop the smudges, the scratches, the difficulty with being cleaned, the gradual degradation of quality. The day that I lost them, they were as crisp and clear, they looked as good, they fit as well, and they worked as well as the first day.
If they cost ten times as much, they ought to last ten times as long to be worth it. And assuming you don't sit on them, lose them, or get into a bike accident with them on like I did, they should do that easily. But even if they don't quite last that long, they might still be worth it. After all, ten pairs of cheap sunglasses that are smudgy and unpleasant to wear for at least half of their lives is not as nice an experience as one pair that's wonderful every day.