UPDATE

Last weekend I sent a specific question to S&W asking whether or not MIM parts can be polished for action jobs:
"A true action job, I'm told, involves polishing internal parts, and maybe new springs. But, some say MIM parts can't be polished for that purpose because it tends to ruin the natural surface smoothness of the parts.
"So, can MIM parts be polished for an action job?
NOTE: This is not a slam on MIM parts. I have no problem with them."
"Thanks,"

Got a nice reply (as usual) from S&W today, but they said only that they do many action jobs on "guns that have MIM parts". I replied today as follows:
"Yes, I know you do action jobs on revolvers with MIM parts, but my question was, do you polish the MIM parts for the action jobs?
Thanks"

I'm beginning to think that the answer to the question is pretty close to what srgvaz and others have posted above. In my own words:
Yes, MIM parts can be polished by skilled people for an action job, but generally a full polishing job is unnecessary with MIM parts, and the time, effort and risk are not worth the small reward which can be better obtained by other means.

I'll let you know what S&W says in its reply.