IMO the casual audience has already been reached, its going to be tough to sell another system, especially if the price point really is $300. If the price is really that much, then this thing better offer MORE than what the iPod touch does, I am talking full download store with 1$ games, a free playable demo for nearly every game coming out that can be downloaded, full web browser that actually works, apps, check in apps, location based services, GPS, face chat between systems etc.. The casual audience already has a DS that works perfectly fine, and has a huge library of games for cheaper prices than the new system. If you have played all the good DS games by now, well I don't know what to say, I certainly haven't played all the good DS games yet and I owned the original DS since launch in 2004.
If they released the 3DS around the holidays I would have no doubt it would be a blockbuster, it wouldn't even be a question, but since they are releasing in March I think it may take up until next holiday season for the momentum to really build on this system. Sure you will have the early adopters who pay full price but its possible the momentum may die after that until the holiday season.
Look at the PSP GO, the $250 price tag definitely turned people off on that one, plus the fact that you couldn't buy games in stores.
I am not buying this thing until the second revision comes out, IMO there is room for improvement, there is always room for improvement in a launch product.
IMO its sleazy for GS to take preorders on the 3DS and not even tell us the price of what we are buying (I don't care if the price hasn't been released yet), its just not a good idea to preorder something when you don't even know how much it will cost.