Yeah I have 2 DS's and a GBA, I'd still get a DSi just for those features. Sound editor? Sweet. I'll definitely get a 3DS too, but for the same reasons you say, maybe not right away.
I just prefer to game on PC if I can, and I really only play my DS in waiting rooms, on trips, or during long renders or compiles. Still haven't beaten Phantom Hourglass or Metroid Hunters and I got those on day one.
On topic: game is too damn short.
I am just saying, that you should wait tell they tell you when the 3ds comes out.