vWii does a very simple/crude upscaling (stretching) of 480p to 1080p.
On the other hand Wii just output 480p, and it is up to your HDTV to upscale it to 1080p. Many HDTV does a much better job than what vWii offers.
This is a common knowledge.
So you could hook up the Wii U using component/composite, run vWii and then let the TV upscale it to 1080p to get the same effect?