My OP was really about trainery-type shoes, as that's what I wear nearly all the time.
I have a pair of Doc Martins that I have had for lots of years that I wore when I was teaching, so a few days a week in term time only. I wore them to the last demo I went on, thinking they would be ideal for a day in London spent on my feet, but they weren't. They fit OK. It's just that the "air wear" sole seems rather harsher to my feet than my normal walking trainers.
The Merrells I have bought recently as a replacement for the Meindls have a Vibram sole, which I know is very resilient. I doubt very much that I will wear through that in 18 months. I have had boots with Vibram soles before and then it was the uppers that wore out after lots of years. Probably if I had been a bit more generous with the Nikwax they might have lasted longer still.