In the short term, Mario Galaxy 2 should effect system sales as there will be marketing and buzz that surrounds the game... plus it's a Mario game. The boost should be small though because it is an expansion pack/sequel.
Metroid: Other M won't do much of anything. I expect it to be sort of a flop. Core games like this aren't selling on the Wii. Metroid has never really even been that big of a seller anyways, so I don't know why people are making such a big deal about it.
The real system sellers are going to be those games that are unique. Monster Hunter 3 should be a pretty big system seller. Wii Relax, if successful, will be a gigantic system seller.