You CANNOT no matter how much scaling magically transform a 480p mastered image to a higher resolution. Be it a picture, movie or video game because the game/movie/picture was never coded for it. No matter how "crisp" or "clear" the image looks it's still a 480p image. You CANNOT add graphics that weren't developed in the first place.
You CANNOT make an SD television display HD images. YES you can play with the settings and make the picture look nicer and sharper, but it will never be able to display in HD unless you redevelop the hardware itself
The only way to truly get a REAL 720p image without artifacts is to recreate the Wii system so it can run at the resolution and then redevelop the game/s to display 1280x720 pixel images. This would work but would not be worth the time.
Just enjoy your games. the Wii2 is only 3 years away. It is almost %95 guaranteed it will be HD compatible since Nintendo was waiting for the price of HD to go down.