Wii will peak when it will be priced under $150, IMVHO.
Maybe now it reached a relative peak at the current price, but if next year Nintendo cuts price to $199, next Xmas should be bigger than this one, and if during 2010 they cut price to $149, that Xmas will be even bigger. OTOH, always IMVHO, a cut to under $100 will happen only towards Wii's end of life, so it will sustain sales some more years but it won't produce new records.