One thing i'd like to give my opinion about is why the wifi isnt working, people are wondering if nintendo might have banned people with the fake save file so thats why they are not connecting, that is almost impossible, nintendo or any other manufacturer, would never be able to do this kind of thing in 1 or 2 days, for many reasons.
First cause they dont really care, second they probably wouldnt know already how to identify size modified save since this was never necessary before, and third and most important, even if they sorta came up with a patch to find who was using fake saves, they would need months of testing to make sure they wouldnt ban legal users, they would never simply release something in 1 day that could ban the people that bought the game, u can take wii firmware 3.3 as an exemple regarding this.
So surely wifi isnt working for compatibility issues with the smaller save, the game probably does some checking to how much space u have left to download songs, and when it notices there is no space at all it starts acting strange, thats why wifi and editor mode wont work correctly, and probably will only when developers release new firmware supporting this new save files.