My husband wears button-down collar shirts to work, and, while the rest of the shirt will still be fine, the collars tend to wear at the fold. I've found I can flip the collar by (carefully) taking out the stitches and then turning it over, and sewing it back.
You have to have a sewing machine for this, and I use a 12-stitch per inch or even higher to resew the collar. Also, check under the collar first to make sure there are no numbers stamped on the fabric.
When you flip a button-down collar, the buttonholes line up perfectly with the tiny buttons on the shirt. Just this week, my husband was ready to toss a couple of cotton shirts that he really liked, because the collars had tiny holes in them. The underside was fine, so now he's going to get at least another year's wearing out of the two shirts.
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Betty's tip about cutting her husband's frayed cuffs off and making long sleeves into short, reminds me of how I have extended the life of some of my husband's nicer shirts that have frayed collars.
