worthwhile buying a JR pass?

If you are traveling in February, you would not be able to use the new JR Sanyo Sanin Area Pass, which would save you a lot of money.

http://www.japan-guide.com/e/e2361_sanyo_sanin.html

Nevertheless, instead of a full JR Pass, look into a JR West Sanyo area pass:

It is much cheaper although I think you'd have to buy the bus tickets to go to/from Akiyoshido (which is mind blowing) out of pocket.

Hi there,

Looking at normal fares.

Kansai Airport - Hiroshima ¥ 12,050
Hiroshima - Miyajima (return) ¥ 1,380
Hiroshima - Akiyoshidai (train to Yamaguchi ¥ 5,590), JR bus from there ¥ 1210) (double return to Hiroshima) ¥ 13,600
Hiroshima - Kansai Airport ¥ 12,050

For a total of ¥ 39,080, the 7 day JR Pass is ¥ 29,110, so you could make ¥ 9,970 in savings over normal tickets. Additionally the JR Pass is valid on the Hiroshima sightseeing bus, so you can explore the city without additional cost.

Hope this helps,
Daniel