I will get it for 20. As much as I am absolutely loving TP, and it is probably my second favorite Zelda game (behind LTTP contrary to most peoples' favorite Zelda), I just finally, FINALLY finished Wind Waker last night, after being in the final rooms of Ganon's Tower for months (work started and I just plum forgot really), and while the Wii controls are definitely as good if not better, they are also different, and there is something to be said for the nostalgia of the gamepad controls.
Also, Wind Waker had an absolutely gorgeous ending, and for one reason or another, it kind of motivated me to give my Gamecube one last Zelda game.
In a lot of ways, even with backwards compatibility, the Wii could never replace my gamecube.