I don't have a Wii but I do have two thoughts on this.
1. One reason to buy the games you already own would to do A/B comparisons on them and see how close the Wii's emulator really gets. You say Soldier Blade sucks on the Wii? Dig it out and prove it!
2. What if Nintendo could find some fool-proof way to verify that you have the actual games (such as mailing in a UPC from the box or something), and when it gets verified, they beam the credit to download that game to your Wii free of charge? That would be cool, but I can't find a way to make it work without the criteria for judgment being easy to reproduce and/or being detrimental to the collector's value of the original game.