The difference between 480i and 480p is negligible on a CRT as a CRT can display interlaced sources properly without conversion. That's the beauty of CRT tubes and rear projectors: they're not fixed pixel displays and can display a source in it's native format without needing to scale, de-interlace or otherwise resize the image.
CRT tubes are needlessly bulky for being as small as they are and if you go flat screen and/or widescreen the weight to screen size ratio is going to be that much worse! I still have an old 27" toshiba cinema series (standard def) tube that I keep around for classic games and Wii looks great on it but not to the point that I wouldn't just want to play it on one of my HDTVs. Standard def tubes are much cheaper (and lighter) and easier to find as just about everyone had one. I really don't think you're going to notice much improvement with an HD CRT tube. Of course, you could always go CRT rear projection! All the benefit of a CRT tube with a more modern screen size.
Personally, I'd rather just dedicate an inexpensive 42" 720p to the endeavor and call it quits. Panasonic plasmas have ~16ms of lag which is practically non-existent. You may even be able to find a used EDTV plasma (480p) for a decent price but you're still fixed pixel so there's really no reason not to stick with a 720p as the PQ will undoubtably be better on the newer display and you can use it for things other than Wii.
What to do if you find yourself stuck with no hope of rescue:
Consider yourself lucky that life has been good to you so far. Alternatively, if life hasn't been good to you so far, which given your present circumstances seems to be more likely, consider yourself lucky that it won't be troubling you much longer...
-- Excerpt from the Hitchhiker's Guide to the Galaxy.