I doubt that you will have much luck with MB doing any "goodwill" for you considering the age of the wheels. Not to say that the wear you describe is not premature, just that lately, MB doesn't do much to rectify individual problems these days.
My 30K mile (at the time) SL developed a split on the convertible top window. Hardly expected, considering the pristine condition of the window and top, and the lack of inclement weather in Texas.
Took an MB rep to intervene, and even with that, I still had to eat some of the replacement cost...and of course, it was NOT covered under Starmark
.
The dealership will probably not do anything for you on their own. You need to get them to contact an MB rep. The best you can hope for is that they swap out the rims and you would pay for the use of your current rims for three years (kinda like tire warranties). I believe that they will cite wheel abuse and neglect (your inclement Iowa winters and use of caustic salt chemicals on the road) and deny any claim.
I will admit that I have seen pitted rims on vehicles that have endured those conditions, but it usually takes five or more years of that exposure, coupled with the lack of wheel care during that period.
Still, see whether you can make any progress there before you go ahead and spend any money on reconditioning the wheels.