Is a GameCube Controller Worth It for Wii Gaming? Yes, For Specific Games
Yes, If You Play These Games
Super Smash Bros. Melee / Brawl: GC controller is the competitive standard (low latency, analog trigger, notched sticks).
GameCube Library via Backward Compatibility:Metroid Prime, Mario Sunshine, Wind Waker, Luigi's Mansion, F-Zero GX, Eternal Darkness — all designed for GC controller.
Wii Games Supporting GC Controller:Mario Kart Wii, Mario Party 8/9, Super Mario Galaxy 1/2, Twilight Princess, Monster Hunter Tri, Tatsunoko vs. Capcom, Call of Duty (Wii), Guitar Hero / Rock Band (with adapter).