If you're looking at watching RDCT, I would say that you really should watch it where you can see the castle because not only do you get to see the projections on the castle, but there are other surprises that can only be seen if you are able to see the front of the castle.
If you're looking at seeing Magical, I personally don't think that you need to see it in front of the castle. The projections are not that spectacular and the only thing special and unique about Magical is Dumbo. So unless you really want to see Dumbo fly (or if you've never seen Disney fireworks before...in which case, you need to get the full experience), then I say watch it from ROA.