Ah, okay, I can see why you'd want to go to USJ, then. If you don't know,
US Hollywood will have it in 2016.
I don't think its worth going to Himeji just to see the outside of the castle and some of the keeps, but since it just past Kobe on the bullet train, you could stop for 2 hours on the way south (or the return) if you were going to Hiroshima. An alternative is Hikone castle, which would likely be a day trip from your Kansai base.
Can you believe I've been to Kyoto twice and haven't made it to Fushimi Inari or Kiyomizudera?