Hit.
In that it is essentially a replacement for Wii Fit. Under the assumption it's being bundled with the Balance Board, it's a first day purchase for a large percentage of new Wii buyers.
If it was only sold separately, it's a different story as most new Wii owners would be fine with just the copy of Wii Fit that came with the Balance Board that they bought along with their console.
I'm actually kind of curious as to how many owners of Wii Fit go out and buy Wii Fit Plus. $20 discount price or not, if an owner is no longer actively exercising with Wii Fit (and the Balance Board is in the closet), I have a hard time seeing those people rushing out to buy the update.
What I don't see happening is an explosion of console sales due to Wii Fit Plus. The $50 console price drop goes further in opening the market to the sub $200 consumer demographic.















