WiiFit with the Balance Board is similar to how I see WiiSports with the Wii. It's a half-decent game that introduces you to the basic features of the product. We all knew that the Wii had a lot of potential before it was released, and based on the WiiFit commercial, it's without a doubt that the Balance Board has a lot of potential as well.
However, unlike the Balance Board, the Wii had a line of launch games (including Twilight Princess) that made its potential a reality as soon as the Wii hit the shelves. It seems that the Balance Board will not have that luxury. So until more games are announced that implement the board, I doubt its sales will soar as high as Nintendo hopes.
Also, is 70 dollars such a high price? Many Wii owners have easily spent hundreds of dollars on games alone. 70 bucks doesn't seem so bad after you make the comparison. Moreover, I'm hope when more games are released for the Balance Board, Nintendo will make decision to sell the Balance Board without the WiiFit. This will allow individuals to save a little bit of money from not having to purchase WiiFit. Additionally, as multiplayer games are released for the Balance Board, households will not need more than one copy of WiiFit laying around.