I'd consider a day (or half-day) trip to Nara from Kyoto. Its only an hour by train, and gorgeous. I'd also consider a half-day stop at Himeji castle, which is right between Kyoto and Hiroshima. It is the best castle in Japan.

However, if you don't want to be moving around as much, it is definitely a good itin- You'll have plenty to do in each city.