Right, we have now spent 3 hours this afternoon playing games and playing with settings.
The outcome is that there is very little difference (PQ wise) between outputting from the Wii in either 480p or 576i to my display.
The only plus that my wife and I could see was that 480p does give a sharper image on Tennis where the ball is concerned - as in the motion is sharper than when set to 576i. All other aspects were indistinguishable to our eyes but then the graphics are quite simple compared to full blown monsters like the PS3.
The only thing I have not done yet is to alter any display settings for that input on my display. I was toying with connecting the Wii via my amp, but I like to keep everything direct which I can at the moment (all 3 HDMI's and Component now in use) and then use my Harmony One remote to control everything (bar the Wii). I do plan on getting a PS3 so then that will have to go via my amp as I have no spare HDMI input left on my display.
I will update further if there is anything else to report.
Thanks again for the replies guys.
Cheers.