Quite right Ehso & Goodyear..
Substances do change with time, even our bones replace themselves every few years. But does it matter? There is so much myth out there with no data to back it up & not surprisingly the myths tend to favor spending more money on things (nutritional supplements, grass-fed, frequently hugged meat/produce, organic food, shoes no older than a few months, I "need" a $6000 mountain bike)
Not that a person might have other reasons for making these choices (e.g. might want the animals they eat ethically treated, might want to increase financial support of a footwear manufacturer), I have just not seen any credible data to support these practices from a general health or foot health perspective. Or a sponsored professional athlete might want an expensive bike as the 1/2 pound of weight savings might make a difference in race money earned or same with current running shoes.
Thanks for the input all. I'll feel confident on my casual run today!
If I decide to keep my shoes for a few more decades I'll be sure to pressurize a container with nitrogen as per Goodyear's recommendation :)