I don't know what your threshold for pain is, but I'll tell you what I see are the advantages.
First, I wear glasses and cannot wear contacts. So, I NEED prescription sunglasses.
I've got a pair of Smiths copper photochromatic (lighten/darken with sunlight). They are glass, and extremely clear -- I always notice how much brighter they are than my day-to-day plastic glasses with all their micro scratches. I really like the fact that they change density. When the sun starts to fade, they lighten up and that's a real plus to me. They're not particularly dark at the other end, which I like since I'm in the shade a lot of the time. I mostly fish for trout in streams, and can't imagine being without polarized glasses.
To the original poster -- it's already been said, but give Smith a call. They just replaced my frames for free, and they're about 8 years old. Free. I asked them for a case (the original case finally blew up) and they threw in a new one of those too.
So, Randall -- that's what comes with the extra $$$ you spend.