Other options: Kurashiki, Okayama, Himeji (you could stop en route)...

And again, Miyajima could be perfect for a 2-night stop -- it all depends on you!

Do you think 3 nights at Miyajima would be way too much? I might be more inclined to go down there if we stay longer, but don't want to stay longer if we'll run out of stuff to do. I've found some hiking maps and it looks like we could fill a 2nd day with hiking to the beach and kayaking maybe? Just not sure about that. I don't want to get there in the afternoon, spend an hour walking around and then think I made a mistake by planning 3 nights there.

i still haven’t been to the 9/11 museum. I have no desire to see that, and I haven’t yet decided whether I really want to visit Auschwitz. The DC Holocaust Museum was enough for me. But Hiroshima was wonderful to see because it’s a story of a city that had to rebuild itself, and chose peace. I highly recommend it since you’ll be so close.

i think 3 nights on Myajima would be great. You’d feel like you had plenty of time to do everything. I don’t think you’ll run out of stuff to do unless you’re the go-go-go types. You definitely won’t feel like it’s time to go
after an hour. But as always, it’s a question of where else that night could be spent... you didn’t give us the “or” so I don’t know if a third night is what I’d choose.

i really enjoyed Kurashiki so if that’s an option I’d probably do that over a third night at Myajima.

My plans aren't firm yet so at this point it looks like it might be Miyajima OR Kiso Valley day trip from Nagoya, plus maybe another night in Nagoya to see Hikone castle. I'm trying to avoid moving around every 2 nights, but it would be possible to have 2 nights in Nagoya and 2 nights in Miyajima (but then that's one day less in each of Osaka and Tokyo), or no Nagoya and 3 nights Miyajima. I've also pondered day trips from Miyajima, like Iwakuni. The other concern about Miyajima I have is crowds. We'd be there the first week of July (not a weekend though), before Japan's summer holidays I think. If it's usually over the top crowded during the day, I'd probably skip it. I can't really get a feel for how crowded it generally is around that time. The idea for 3 nights in Miyajima came from not wanting to move around so much. BTW, marvelousmouse, your trip report was one of the first I read when I started planning. :)