I take the grills off when i really sit down to do some listening. I think they sound better with them off. A little crisper like you say. And my non scientific way of telling myself that it would affect the sound is try blowing through the grill cloth. It doesnt go through like it would without the grill cloth.
That being said, I keep the grills on most of the time now days. I was the exact opposite a couple years ago but i have become attached to the sleek, slim look they have with the grills on. who knew.
