Quoted from RobT:

Exactly right.
Screened is better than decals specifically for the reasons that you mention. And it isn't just on Stern decals. You can see the same lack of depth (blacks) when looking at an original screened MM vs a restored one that has decals on it. The decals simply do not have the depth of color to match the screened print, and it is especially noticeable in the blacks. This is an easy way to spot whether an original screened pin has had decals put on it.
Of course in the case of IM (and Stern in general at the time), the advantage that the screened cab has over decals is greatly reduced because of the pixelation, which will be largely reduced with the decals.
I personally prefer the richer colors, but obviously there are plenty of people who will prefer the higher resolution.