To be honest, you're right Remake version is a lot better, there is a lot more scenes, new stories, new dialogues, better combat style, new ending E thats mind blowing and to be honest without seeing ending E I would feel empty. I feel like without playing ending E (thats only in remaster version) the game is not completed. Something is just missing, deeper relations.

I'm sure u will get more information about the Kaine/Emil in second playthrough, however I don't know if they will show as much as in remaster version, since in remastered version playthrough 2 changed my way of thinking about the story and all the characters. To be honest endings B/C/D are not that good. The thing thats making them good is ending E. without ending E - B/C/D seems kinda weird and uncomplete.

I believe that the story durning the early-late game is a lot better than endings itself.

and still.... u missing the red bag man story with the ship.. I can't believe it. It was the most beatiful thing in whole NieR universe