It ought to reduce vibration transfer (though I would have thought the bolts would need some sort of isolation as well)
It might reduce blade chop on the grille, but doesn't really add enough spacing. If air noise is the problem, and the case will still be strong enough, hacksaw out the punched grille and use a wire finger guard instead - more airflow, and quieter too!
PS. I made my own spacer washer out of a cork placemat, but it's terrible stuff to work as it fragments so badly.