From someone also middle-aged and with good (but kind of short) legs, here is my "top 10 reasons you should consider trying them" -
1) They are sooooo comfortable!
2) They give you a little added warmth on chillier spring/summer days/nights
3) They give you an extra bit of modesty
4) They enable you to extend the life of those short dresses you may still have in your closet - the ones you used to be able to wear when you were younger (even if our legs can still pull of short dresses and skirts, often our butt starts to sag so when we bend over... well, you get the idea!)
5) They act kind of like Spanx... meaning they smooth away lumps and bumps and leave a nice clean line under your clothes
6) They keep the back of your bare leg from touching public seating in the summer (like on the bus etc)
7) Our legs may still be shapely, but the skin might have seen better days. (the skin around my knees has gotten... slightly saggy). And if your skin is still great, the leggings will cover them to protect from sun and keep them that way!
8) Black opaque leggings have a slimming effect. I think my legs look even skinnier in them.
9) They are "on trend." No, you don't need to hop on every trend, but working them into an outfit or two and doing it in a way that befits our middle age, shows that we are modern not dowdy and that our style is evolving. With that said, there's so many styles out there now - if this is not your thing, just pick another style!
10) As Angie advises, treat them like accessories. As such, they add an extra layer of interest to your outfit - which is nice in the warmer months when it may be too warm for a jacket, cardigan or too many other top layers. I particularly like Angie's zipper kind - mine have silver studs - which adds interest too. But even plain ones with no detailing are adding something.