I mean, the nature of the new scenes could be similar to that of the silent scenes in KHFM. You're not missing anything by not watching them; they just provide additional content that describes Riku's time in the Realm of Darkness. After all, they're an extra.
Eh... I don't think these are that "useless". After al, they will be cutscenes connecting Re:Coded to X, DDD and III. Things like why Riku cut his hair off could appear. More stuff about the past could also appear that could give us hints towards the future of the series and to III. I don't think they're going to be some minor cutscenes. After all, this is basically a compensation for the lack of news of KHIII at during this year, so it has to be something worth the wait.