In most cases the hardware does not need or use the extra speed provided by higher-end SD cards, but the Wii may be an exception and there have been no official specs released in that regard. In addition, I read a rumor some time ago that Nintendo plans on releasing their own high-capacity cards specifically for the Wii. I'm not sure if that has since been confirmed or rebuffed, but given the uncertainty at this point I'd wait until you get your Wii to make the final decision.

John


P.S. The manufacturer of the card has some importance as it may tell you how reliable the product is, but aside from that the name on the packaging makes no difference.