With the SD card upgrade, is there going to be downloadable levels for certain games. 

SSBB

Boom Blox

Boom Blox Bash Party

Golf Courses for Tiger Woods

New Maps for games like Wario Land or The Conduit

ect...

I really feel that is the only thing that the Wii is lacking, is downloadable fun.  More game play for games you already love to play.

I am sure this is somehting that Nintendo will be able to offer in future titles. Not to sure about games that have already been released.

Yes and No.
Yes it's capable, No it's not going to happen.

Like all machines that have the ability of a File System that can execute the Wii is capable of having better downloadable content system, but it won't happen. The companies in questioned games have already moved on. For these games to improve their DLC they would need to write a new main executable file and have you download it via WiiShopping channel(for free). The file would probably tick in from 1-5mb.

But the real truth is that companies could have already taken advantage of the 2GB SD card capable at the time and they didn't. I don't see companies suddenly taking the oppertunity now to use 32GB space if they were so inclined.

I find that console developers are a sorry lot of slackers in regards of forging their own features and often wait for the console manufacturer to do the work for them(praise Disney and DGamer, sigh).

So until Nintendo provides a DLC engine and a friendlier DLC shopping center instead of a DLC application store I don't see DLC picking up on the Wii anytime soon.