Metroid Prime 3 is a definite purchase if you're looking for a solid wii game. It is easily one of the top two games on the wii, and a must buy.
On regards to whether you should buy Super Mario 64, I'd say yes, but only if you think you have the money to get it. Because, since wii launch I have beaten through mine maybe 2-3 times. So, I'd say it was a good purchase for me anyway.