I have an invisashield on my Ipad mini w/retina. Insvisashield just came out w/ the new protectors for the back of the device which have a cutout for the microphone, but it does not protect the sides of the device like the protectors did for the original mini. Have a similar HD protector on the front.
The mini retina was expensive and the protectors give me piece of mind, b/c the device is used constantly and moved all over the place.
But i do have a ipad 2 w/o any protection, and it remains perfect. So I guess it's just personal preference. But I do think that with careful use and caring, the devices do hold up quite well.