Re: “The global trend is that people and businesses are not replacing PCs or Macs as frequently as they used to.”
Yes, I think this is true. It used to be that new computers would show a jaw-dropping speed improvement after 3-4 years, but computers last much longer these days.
My first Mac was a IIcx; with a couple of hard drive expansions it lasted me six years before it was too slow and old and I wanted to go to PowerPC.
My second Mac was a 7200. I got bigger hard drives more times than I can count, and after about four years I swapped my drives into a used 7300 and got a G3 upgrade for that, which held on for another four years.
My third Mac was a G4 tower. Again I got larger hard drives a few times, but after about six years it was getting creaky and I wanted to make the Intel transition.
My fourth Mac is a 27" iMac, purchased in 2010. I never pushed the limit of the 2TB internal drive I got with it, and last year swapped in a 1TB SSD which gave me an amazing speed boost. That machine is now eight years old and is faster than the day I bought it.
It will not update to Mojave, so I’m stuck in High Sierra. Is Mojave plus a retina display plus the Bluetooth Low Energy necessary for Continuity really enough of a leap forward for me to put my money into a new machine? I’ll probably keep looking at the prices of systems with a 2TB SSD and whether software starts to show up that requires Mojave or its successors, but at this point I’m not inclined to get a replacement unless forced by catastrophic failure or a significant leap forward in the hardware that I haven’t really thought of.
I’m not completely trouble-free–I’m getting some strange intermittent connectivity problems that I reboot to solve–but I’m certainly not feeling like an upgrade would be worth the cost.