Currently Nintendo has 73 Cover Plates (some people call them Kisekae plate or face plates) for the New Nintendo 3DS(Not *New* XL model). This is not including limited edition ones that were released with various hardware/bundles/promos. The latest face plate #076. Number 073-075 hasn’t been reveal to the public yet. Note this list is based off the releases in Japan and not in North America.
The prices range from 1,000 Japanese yen to 3,000 (approximately $10-$30 USD). In my opinion, having cover plates sure beats getting a brand new 3DS system.
I wouldn’t consider this a shallow move because, just like how we can have new phone/tablet/other mobile device cases, why not have them for our handhelds?
It can also be a fashion statement in terms of styling your 3DS with what fits with your own personal taste.