It's difficult to give any feedback without any specification of your interests. The destinations differ wildly, have their strengths in different time periods and major sights. Basically the eight major day trips from Nuremberg easily done by train are Würzburg, Bamberg, Coburg, Bayreuth, Regensburg, Ingolstadt, Ansbach and Rothenburg. None will fail you but for castles you rather go to Coburg, for baroque palaces to Würzburg and so on.

my primary interests are: architecture, old buildings, fountains, gardens, churches, bridges, castles, palaces, beer, photography, countryside walks ..........