First, this is in the Tips section, where people post tips such as "pack a lunch" or "ask for a cup of ice" or any other useful tips people have found when going to WDW.
You will get a lot more responses to your question by posting it elsewhere - I suggest either the "WDW with kids" or the "Food and Dining" sections.
As for your question, for me, I think the castle is overrated. But that is me. The big difference is that in the castle you are going to get Cinderella characters in Cinderella's castle. In Akershus you are going to get a variety of princesses in a castle like atmosphere.
So if your kids are die hard Cinderella fans, then maybe that makes the castle worth it.
If you want to say you dined in the castle, go for CRT. I’d recommend it sometime once for the experience, but your next trip doesn’t have to be it.
You can still see Cinderella and other princesses at Akershus. If you’re on a dining plan, Akershus is only 1 TS credit, while CRT is 2 TS credits. If you’re paying out of pocket, CRT is more expensive than Akershus, but not by much. Hope this helps.