The value of buying from CarMax is a level of assurance that I won't be buying a lemon and that I'm doing business with a company with a positive reputation.
I'm in my early 40s and I've only had five cars. The first two were from a car dealer who was the father of my best friend, one new one and two from CarMax for myself and my wife. My experiences at CarMax were much better than my one time buying a new car from a dealer that I didn't know personally.
I've never used CarMax but I'd definitely consider them if I wanted a used vehicle. I'm in a similar situation when it comes to keeping cars a long time. If anything, I tend to keep them for an expensive repair job too long.
It does make the car buying experience easier. I know the trade-in isn't worth much and I can always just donate as a fall-back. I also haven't needed to finance for a while. When you can just basically ignore the dealer number BS and go in with a take it or leave it price based on the invoice, the experience may still be annoying but it's not particularly stressful.
I've never done a trade in. My first car I gave back to my parents, my 2nd one was totaled, and my third one I gave to my son. I've gone to CarMax both times with a preapproved car loan but they have always had a lower interest rate.
I'm in my early 40s and I've only had five cars. The first two were from a car dealer who was the father of my best friend, one new one and two from CarMax for myself and my wife. My experiences at CarMax were much better than my one time buying a new car from a dealer that I didn't know personally.