No question about the M&H products being high quality tires. And you have clearly taken good care of them.
I'm not a tire expert either, but I work at Ford and was here during the whole Explorer / Firestone fiasco. Some of the lessons learned from that experience were that 6 years is the longest you should run tires on a daily driver, and 10 years is the longest you should use any tires, no matter how good they look. I'm probably going to replace the Nitto NT555s on my '97 this year, even though they have lots of tread life left, because they will be turning 10. Don't know if you have any interaction with Discount Tire stores, but they will not touch a 10 year old tire, even if they sold it to you.
1997 Thunderbird Sport
5.0L-2V PI S/C
540 RWHP / 492 RWTQ
11.28 @ 123 MPH