Good news, stuff should just work, bad news, nothing special gets added.
That is a bit of bad news. I would have really liked some up-scaling on my Wii titles, especially since they are going to be fed through the Wii U's HDMI output. While it will still be a touch more convenient (I currently have to feed my Wii directly into my TV, instead of through my surround sound), 480p is so last year.
I imagine that part of Nintendo's reluctance to properly upgrade their backwards compatibility lies in an experience they've already had with the Wii. Such effort would kneecap their ability to re-package previous generation titles for their new system. They did this already with several of the more popular titles on the GameCube. I imagine they will do the same for some of their better selling Wii titles.