I'm not quite sure I understand the point of having the series boxes, but I suppose the odds are better now (1 in 18, 1 in 19, 1 in 21, and 1 in 66 opposed to 1 in 124), which could help folks that only missing a few emojis. Maybe they'll be doing something in the future (e.g., "Use a Series 1 emoji to clear 500 emojis" or something like that). For now, I don't really have much of an opinion about the boxes.
It looks like both Sora and Aqua are Diamond Box Exclusives. We get one Diamond Box at the end of the event, but if folks want both new emojis, we'll need to buy at least one Diamond Box. I don't really know anything about Kingdom Hearts, but I suppose the completionist in me will end up trying to get both by the end of the event.