As to Cinderella's royal table, there is just something really special about eating inside the castle. It's a very small restaurant so it is a very intimate setting. Also tips are included, which also adds value to the fact that it is 2 credits. So, I do think it's "worth" it. The question is whether you would prefer going there vs. two other restaurants.
I would strongly consider the new character meal breakfast at Boardwalk, the Bon Voyage breakfast.
Also, I would not use
DDP to pay for Trails End buffet. I would pay for that one OOP, and then use the extra credit for a character buffet. If you look at the prices here, I would say that Trail's End is not worth 1 credit, given the price per day of the DDP. In general, $35 per adult credit is the tipping point for a table service meal to be "worth" 1 credit. Cinderella's royal table is over $70 so worth it. Also, by going to Cinderella's royal table, you will not have to pay tips for the two meals you would otherwise do, which saves quite a bit of money, also.
https://www.disboards.com/threads/buffet-character-shows-aycte-pricing.3108466/
As for brunch or dinner:
1. Akerkshus: look at the dinner menu. While the cold buffet they have is great, the family style meal is "regular" breakfast foods. If the dinner menu looks appetizing for your family, I would switch this one.
2. Donald's: the breakfast buffet here is among the most interesting/diverse buffets. However, I *think* it would be similar to the Boma breakfast, which you are already doing. So, I'd stick to dinner.
3. 1900 PF. Great breakfast, and also great dinner. However, the characters are not the same. Would you rather see Mary Poppins, Alice, mad hatter (and 1 other, I think) for breakfast, or for dinner: Cinderella, Prince Charming, the step-mother and step-sisters? The step sisters and step mother are GREAT, so I would pick absolutely pick dinner at 1900 PF for the characters. Best character interaction we've had was dinner here.
4. Crystal Palace is the same, to me, for breakfast and dinner. Both are very good, but neither menu stands out above the other. Characters are the same.
So, if it was me, my choice of 8 credits would be:
1. Akerkshus lunch or dinner
2. Cinderella RT lunch or dinner
3. 1900 PF dinner
4. Donald's dinner
5. Boma breakfast (though this is under the $35 also)
6. Coral Reef Dinner
7. Bon Voyage breakfast
Pay out of pocket for Trail's end (you will be paying OOP for some meals, anyway, and this one won't cost that much more)
I would go to Be Our Guest for breakfast or lunch (or both) as that is a quick service credit for those meals. If you are planning 2 days in MK, I would do one of each.