I didn't see the point, as I didn't buy many DS games, or if I did, never bothered to register them. I know they have some exclusive rewards, but I didn't really like them.
Good luck with that. Getting the amount required to get that will take an insane amount of purchases that it will be cheaper just to eBay it unless you buy a lot of Nintendo shit naturally anyways.
you can also get points from Wii things and wii console. Also beware the points expire after either 12 or 24 months - can't remember - so you can't just sit and wait until you have enough points for some limited edition zelda figurine as your points will expire and dissapear