I think that is just so cool and nice that you also shipped the gift for your niece and left the gift to her from Mickey. I will have to keep that idea in mind.
We took a train to Florida when I was a kid. There were some boring sections but overall it was a scenic trip, although there were some problems and the trip was quite long. We were going from PA to Fl.
I think I would use the dining plan. It would just make things easier for me. As long as there were more than one or two items on the kids menu, my little one is young enough yet that she probably wouldn't mind so much.