I have an intel chip from 6 years ago and I still feel there is hardly any reason to upgrade. It still does everything I need it to do very well. I upgraded my gpu that was about 5 years old and I saw about 3x the performance.

The last few years have been mostly about performance per watt. I changed my notebook a couple of years ago, jumped from an i3 3200 to an i5 7200U. I got 80% better performance (on numerical code) at 15W, instead of 35W for the i3. Unfortunately manufacturers cheaped out on the battery, so I went from 6 cell to 3 cell, for about-ish the same battery life I had on my previous notebook.