It's pretty unlikely you'll _accidentally_ buy component cables for the Gamecube. Those things are worth a fortune compared to composite cables. They also plug into an entirely different port, which your Gamecube might not even have.
(As an aside: the reason there are no third-party component cables is because they need to have a DAC in them, since the "component port" outputs in digital, not analog.)
That said, component is definitely the way to go on the 'cube, if you've got the cash, the appropriate GC model, and a 480p-capable TV. Progressive scan really increases quality substantially, and it works on most games.