"If the TV has no input aside from coax, that means one fo two things. It is either of such low quality that you have far larger image quality issues than how the Wii signal is getting to it, or that the TV is so old that no matter how good it used to be it is so far out of whack calibration-wise that it's degraded performance is the main issue."
Stop being a idiot, not everyone has to game on a 50" $5000 hdtv thats replaced biannually like some of the people here. I've seen plenty of CRT's dating back to the 70s that are used even now by people that offer pretty good picture quality if you don't mind hooking up something by coaxial connections.
Its only been fairly recently where low end CRT's even had composite inputs as standard, it wasn't very long ago that coaxial was basically the standard.
I've never noticed a huge leap between RF boxes and composite when the RF box is in good working order, sadly they always seemed prone to interfance and degradation pretty quickly for me which is why I'd suggest you avoid it if you could, even if it means hooking up a 2$ thrift store VCR to this tv so you could hook the Wii up to the VCR via composite, then coaxial to the tv. Would help a little bit.
"Uh go to Wal-Mart and spend $100 on a TV, if you can't do that then you probably should have bought groceries or paid your utility bill bill BEFORE you bought a Wii."
Buying a new tv because some AVS user things people should be executed at dawn the day after buying a new console without a new tv to go along with it is stupid, leave the guy alone.