Re: Iwama or Tanabe
I haven't been to Iwama, but I think that Szcepan is correct - skip Tokyo and go directly to Kyoto. You can get between the two in 2.5 hours on the Shinkansen, but it's a pricey ticket. Nara is an easy day trip from Kyoto and well worth the time. Himeji Castle is a little farther, but can be done in another day trip.
Tanabe is a small city with nothing much to recommend it except, of course, for O'Sensei's grave. That being said, I would highly recommend traveling further into the Kii Pennisula. The scenery is fantastic (mountains, hot springs, etc.) and the area is the home to many ancient Shinto shrines. One of the main shrines, Kumano Hongu Taisha (in Hongu) was considered by O'Sensei to hold the 'spirit' of aikido. Hongu is a short trip from Shingu, and I think there is a bus you can take. My favorite was Tamaki Jinga, but that's a 90 minute drive up a steep windy logging road (paved) - you'd need a car and GPS!. Shingu is on the coast and there is a train that goes all the way around the penninsula from Kyoto (passing through Tanabe). There is a lovely shrine in Shingu, as well as Kamikurasan (a shrine by a huge bolder at the top of a bluff), and Nachi Falls is a short drive.
An itinerary with 5-7 days in Kyoto (with possible day trips) and 3-4 days down on the Kii Penninsula would give you a good taste of modern and ancient Japan, along with some aikido related stuff. If you go to Shingu, you may be able to visit the late Hikitsuchi Sensei (10th Dan)'s dojo. They have a full schedule of classes, both evening and morning, and have had many non-Japanese visitors. Call or write, however, instead of just showing up at the door.