That's a good question.
From the standpoint of a US Wii, all of my Virtual Console games (via component) output at 480p when my console is set to 480p, even Super Mario Bros for the NES! At least, that's the resolution my TV gives (480p).
If your TV is a CRT, you'll notice little difference. If it's anything else, it should have a decent deinterlacer in it to make it progressive as it is -- with a native progressive image, there will be more visual detail as opposed to interlaced, and the image will never split up horizontally with fast motion.