Glenn,
IMHO, it depends on your use. I shoot my steel anywhere from 3 yards (well under manufacturer recommended distance) to 700+.
For rifle practice and handguns at distance I wouldn't worry about it, for the close up stuff I want steel that's perfectly smooth. Once/IF my plates get dimpled/cratered, they're moved back to a static stand and used for rifle practice only.
This is one of my AR500 plates that I've used for about 8 years and it's still in great condition:
It sits 200 meters from my bench. Here's my PIG in "AR500" it was cratered/dimpled at 200 meters, I suspect the steel isn't quite AR500 or it had a couple softy spots. There are small dimples on it. It's strictly a rifle target, but often gets shot by handguns at about 25 yards or so (it sits on the back of my pistol range). So far zero issues:
A big thing with steel besides hardness (and shooting with the right distance for caliber/velocity) is how you mount it. Generally a downward angle and the ability to move when hit makes your steel last longer.
So I mount my stuff on chains, with springs, or on target stands that allow them to move. Here's a spring set up:
Having shot on several ranges with imperfect steel targets and gotten hit by "shrapnel" I now keep my close in targets as smooth as possible, and mounted at a downward angle.
It seems to work.
Chuck