If you wanna delete ALL of your saved data then do this...
-Will delete VC Games, Channels, Data, and Mii's,
WARNING, DON'T DO IT UNLESS YOU REALLY WANT TO.
1.Go to Wii Options on the Menu
2.Click on Wii Settings
3.Go to "Format Wii System Memory" (page 3)
4.Then Click "Format"
Also what you mean by "fooling around with saved data?" Can't you just delete the miis or just edit them?