If you do want a "Princess" vacation, I would do both. I have been to 1900 Park Fair DINNER and they had Cinderella, Prince Charming, Fairy Godmother, and two mice. The food is the best buffet we've ever tried at Disney.
The Norway lunch and dinner have the rest of the "Princesses", I hope including Ariel. I'm doing both with my niece in November. I wouldn't duplicate the castle and 1900 Park Fair dinner OR for that matter with Norway either. The castle breakfast has Cinderella, and several other Princesses, so doing the castle with either one will duplicate. I don't think there's any duplication with the Norway and 1900 Park Fair. You can order the slipper at 1900 Park Fair dinner.