Quick clarification regarding the buffets:
the buffet selection during dinner is completely different in each Buffet restaurant, but each individual buffet does not change their choices each day. So each day, the choice will be the same , more or less. Exemption is the Yacht Club Buffet, which has themed evenings.
Regarding Breakfast: choices are vast really , but do bear in mind that Germans normally have a cold breakfast with the typical charcuterie (choices are way more than on American vessels)and breads. you can always opt to have a sit-down breakfast in French Kiss, with nice choices and great presentation.
In General, Aida is not a step-up from MSC or Costa. Where did you get that idea? It is a different concept, but also mass-market and especially kids friendly.