Have to agree it's a wonderful area - and you're right about the fall. Some of my best fall shots (from our trip 10yrs ago) were from the maples in the Chuson-ji complex at Hiraizumi and our best ryokan experience was at a hot spring in Aizu Wakamatsu (Higashiyama Onsen). My photography skills have come quite a long way since then and we plan to return one day...
Cheers
Andy