I was going to use Savegame Manager GX to transfer my Miis to my original Wii, but then I learned that the application is buggy with the vWii. Is there any easy way I can transfer my Miis to my original Wii?
Yeah, exactly. The Wiimote can store information, and Miis can be stored in it.
You go to the Mii Plaza and click on the Wiimote icon, then choose the Wiimote you want to use for storage and then drag and drop the Mii's you want. You can save up to 10 at a time.
The above one is a valid option (note that you need to install a proper Mii Channel instead of the crippled one preinstelled on Vwii to get that option), alternatively you could try good old Mii Extractor and Mii Importer by Waninkoko
Any time it looks like you're in an unwinnable situation that will require you to restart the entire game, it overwrites all your saves with that autosave.