I don't think it's economical to go for the Best Of The Best Of The Best in the hopes that you won't have to upgrade for a long time.
I suspect that, usually, it's better to go "pay 50% of the price of the top chip to get 80% of the performance" and maybe make less expensive upgrades a little more frequently.
But, what do you define as a "long time" to not upgrade?
Among PCs I've owned, what was a beast of a system in 2008 performed more or less what a low-end budget system performed in 2016-2017.
Things flattened out through generations of Intel CPUs because of lack of competition from AMD until recently.
But, my son games at his mother's house with an i5-2320 combined with a GTX 660Ti 3GB, on a 1920x1080 screen. (PC purchased Feb 2012, GPU was admittedly gotten for free from someone about 2 years ago, though prior to that it had a mid-range for 2012 gpu that I'd added)
He uses an i5-6400 with an R9 285 (previously R7 250E) at my place on a 2560x1080 screen. (purchased a little over a year ago, previously he had a budget small desktop system)
I'm using an i5-4340 with a GTX 1080, but that graphics card was mostly so I could game reasonably on a 3840x1600 screen (I needed the horizontal resolution for work purposes, though. Purchased PC Jan 2015, added some more RAM later, got the R9 285 when I got the PC, but then moved it to my son's PC when I got the GTX 1080 for my system in Feb this year).
While I sometimes consider upgrading my PC (more modern CPU/MB/RAM), to be honest, I don't think any of my use-cases need it. It would have to be an insanely good deal for me to consider it.
For my needs, these machines have lasted.
Do you have a PC currently? Is it lagging in anything you're using on it (games or otherwise)?