The ski hole is only useful if you have the rear folding armrest imo. On the other hand, having the metal punched out can be useful in other ways like carrying a half dozen 2x4's in your car extending from the trunk through the hole and out your moonroof.

If you're a true audiophile, chances are that you are going to have most of your soundstage and main speakers up front. If you don't have any rear speakers or don't have the need for them, you can just leave the grills and ditch the rear speakers and have the bass port through those openings as an alternative.