Wii U will be not more than $250.
If the streaming to the controller functionality works near perfect and you can play your console games on the controller even if the tv is off then it will have some extra serious appeal to families.
Last year's demos didn't look exciting.
But they have had a year since then to work on software for it and probably didn't show every killer idea that they had.
I see no reason why it won't end up selling halfway between what the Wii and GC sold just based their 1st party strength, new controller and culture of being creative with their franchises and highly polishing their games. Oh and also it is the first time they have done HD which I have a feeling will bring some reluctant fans out of the closet.
Still I don't expect more than a 1st party games machine. Doubt 3rd parties make exclusive titles for it.