I thought the grill/cover was a moulded perforated type of plastic. How bad is it?  Maybe just stick an ‘ouch’ sticker over it if it’s not too big and live with it. I guess these things depend on how it makes you feel and my own OCD would likely mean I would suffer, at least until one of life’s bigger problems emerged.  As many would say, if it doesn’t affect its audio performance then maybe camouflage it as best as possible and replace it a little further down the line when you’ve had sufficient use from it, or at least until the next generation of the Arc emerges from the Sonos labs.