Wii VC is extremely good. Wii U VC is, apparently, another story. I only have two games for Wii U VC but I've spent much more time with Wii VC. My opinion is that the Wii is probably the best box for outputting old school video that you could imagine. Quality is ROCK SOLID when using component video and an SD set. If the NES Mini does exactly what the Wii VC did but over HDMI then it's absolutely worth the asking price.
Regardless, NES/FC Mini and the Wii and even the Wii U crush any NES experience we had in the 80s and it does it for about the cost one NES cart. This is a pretty easy thing to buy with confidence.