I've argued in the other thread that even a16GB Slim+Move+Wonderbook could sell well for around 225 (after all that's how much Kinect is selling for) if there is a big marketing 'be like Harry Potter/help your kids read and have fun' marketing push.
Other than that I'd say you're right the 16GB model has to be below 200 and a bundle with a kiddie game for Christmas is the way to go. We'll have to see though, because even LBP karting or PSASBR or Sly aren't exactly kiddie friendly (well the 3-10 year old category that Nintendo has). However, Sony's London studio which does most of the casual games (SingStar, Home, EyePet etc) usually announces games at Gamescon and releases in the same year.