Yes, it's soft steel, but it is steel nevertheless. I have a 5946 that I shoot regularly with Silver Bear. I've put several thousand rounds through it. I have another 5906 with about the same round count that I haven't shot in a while. That one was only fed a diet of brass cased ammo (before the '09 craziness). There is a difference, though not significant. You can tell the difference in wear under a flashlight. The extractor claw from the 5946 is a bit more "polished" at the edges.
There is another reason aside from the hardness of the steel case. Steel cases are harder to extract. Although they expand less than the brass case, they also don't contract as quick. After about 4 or 5 magazines (continuously), I will start experiencing FTE's every few mags. I don't rapid fire, so that might make a difference. Also, it's a S&W so it's probably not meant for steel case.
Overall, does it really make a difference at the range? Probably not. An extractor is what -$10? Does it wear out anything else quicker? Not as far as I can tell. The benefits outweigh the cost if the shooter doesn't reload (and wear breathing protection when shooting crap like Brown Bear).