I don't know...
Nintendo knows Mario games sell a lot by themselves.
The regular Mario stuff, will probably keep being Mario only.
I don't think we will see a lot of M&S games, but the ones we see will be something different than most other games.
For sales on this one, this game is huge. Huge, as in bigger than any Zelda, and perhaps bigger than any 3D Mario game. Except for MKWii perhaps (and SM64 if you count the DS one too)
Combined, after 20 weeks out, they are less than 100K behind Super Mario Galaxy.
From week 20 to 30, the Wii one sold about 50K less than SMG. The DS has only been out 10 weeks, but it should sell at least 400K, making it track ahead of SMG.
Will it catch SMG you ask? Easily. It is 100K behind LTD, and it is 30K + more weekly. Combined, the 2 could be close to 750K ahead of SMG by the end of the year.
I would even go far enough to say that the Wii one could fight the 360 version of GTA IV, and that the DS one could fight the Ps3 version.
I expect both of them to lose those fights, but they could come close.