Is Hiroshima and Miyajima worth adding to a first Japan trip?
Yes, if you can treat them as a proper western extension. Hiroshima and Miyajima add real depth to a first Japan trip, but they work poorly as a long, tired box-tick from Kansai.
Answer
Hiroshima and Miyajima offer a different kind of weight from Tokyo, Kyoto and Osaka. Hiroshima asks for emotional attention, not just sightseeing time; Miyajima gives coast, shrine atmosphere and a slower island rhythm when the timing is kind. Together they can be one of the strongest additions to a first trip. The catch is time. Trying to compress them into a single overlong day from Kansai can make both feel rushed and strangely flat. Stay overnight if you can, or cut something else rather than pretending a meaningful place deserves only the space left after every famous temple.