I would second the trip to Fukuoka. Spend one or two days in Fukuoka instead. It's a very lively city, with an amazing night scene (yattai, bars & restaurants, etc.) and it's quite a bit more fun than Hiroshima...in my opinion, of course. I had the most relaxing part of my 2006 southern Japan trip in Hiroshima, but I was a little bored, too.

Fukuoka Travel Guide - http://www.japan-guide.com/e/e2161.html