When all is said and done 3DS could be at 80m ltd. How is that a disappointment? Nintendo lost a lot of the handheld market to Apple and Samsung. I think 80m is great, all things considered. I think just a plain DS part II wouldn't have sold as well without some kind of marketing gimmick.
I agree with most of what you said. But, it's not a gimmick to Nintendo. From their perspective, it's a feature unique to their handheld platform. And one that they have been working their way towards realizing for some time now. They wanted to add to and differentiate the DS's successor from simply being a DS with a little more power. Aside from the depth of view in games, I've gotten a lot use out of the 3DS' camera over the years and enjoy looking at the pictures I've taken in 3D. When I used the AR cards that came packed in with the system for the first time, I was blown away. I was actually disappointed that AR cards weren't utilized more during the 3DS's lifespan.