I'd like this on my DS if they can fix the bugs. I made a fairly involved track, saved it, loaded it, and it behaved differently. The rider crashed on my first loop for some reason, even though he could make it all the way through before. Also, if I used the flag button to test a part of a track over and over again until I perfected it, it again behaved differently if I played it from the beginning. Still, it's a beta.
The only reason to get it on Wii instead of DS (and I'd hope it would be a download in the Wii Shop) would be to make it easier to share your creations. That would be pretty cool, so it might be worth giving up the stylus.