Like you, I don't 'replace" irons. Bought sets over the years because for one reason or the other, sometimes over 6-8 years and sometimes just because.....
I tend to keep my iron sets. The only thing is, over the years I'm not able to motor the XS shafts in some sets and even the stiff flex is getting difficult to power the long irons ( 2.3 & 4), especially the heavier weighted shafts.
Do not like the regular flex nor the graphite shafts , yet. Who knows, I'll try again maybe in a year or two. I do like the light weight steel in long irons for now, except I need to find the right swing weight to tune in the timing.
Nothing beats a roll of lead tape, irons take 2 gm. to change one swing weight instead of the one gm/swing weight for the woods.. Old school way of adjusting with lead tape on the driving range, to see the distance and trajectory changed with a small change in swing weight.