Curious as to how many miles most folks ride before changing and getting new tires.
Specifically road bike tires 700x23-28 sizes?
I just replaced my rear tire having put on approximately 1200 miles, because it was becoming flatter vs the normal roundness.
Depends a lot on the tire. Lightweight tires get that way by starting with less rubber. Your profile method is probably sound. You can also try to judge if you have the tire off and hold or measure the thickness through the center.
Oxon Hill Bicycle and Trail ClubP.O. Box 81 Oxon Hill, MD 20750-0081