Objectively speaking, NSMB is one of the very, very most successful game series, so it is not over-priced by free market standards. The first two entries sold over 20 million, the 3DS version is well on its way and the WiiU version is close to being the top game on the system despite another one being bundled. Definitely priced right. DKCR also sold extremely well.
Subjectively speaking I am personally very comfortable paying $60 for 2D Mario. I really enjoy the games, and I pay for enjoyment.
I see no reason that a 3D game should be priced more than a 2D game. Games are all the same price no matter how long or how much it costs to make them. They are discounted when they stop selling.
Maybe you should think of games like music? An album featuring 100 orchestra musicians would require far more effort to put together than the latest Beyonce disc. But Beyonce presents a unique talent that lots of people enjoy, so it will sell much more, and at a price that is more or at least equal to whatever some orchestra could charge. When you buy a Mario game, you're paying for the unique talent and artistry that is Mario. And yes, I do think that Mario is gaming artistry. NSMBU is outstanding with fantastic levels, style and seemless MiiVerse integration.
And if you're saying that 2D games should be cheaper for the good of Nintendo, that doesn't make any sense. Their systems have sold like hotcakes and each Mario title makes them about a billion dollars. 2D Mario is their lifeblood, and selling them at a cheaper price would only give them less cash to compete in a tough industry.
