My vacation is actually for Tokyo and the areas south of Tokyo- Kyoto, Osaka, and the Kyushu region. I guess I might wait a few more days for updated news about the nuclear generators before rescheduling.
Keeping an eye on things is the best plan of course. You could try to reschedule a flight into KIX (Osaka) though there aren't many these days. Skipping Tokyo wouldn't be the end of the world (admittedly I am biased as I am in Kansai).
As long as the trains and airports are operating in Tokyo, and I suspect they'll be back to 100% in the next two days, your travels should be unaffected. This is especially true if you are traveling by shinkasen.
Osaka is 500 miles from Sendai, and Kyushu about 900 miles.
A comparison would be Detroit to New York city (600 miles).