As far as domestic F goes, certainly worth it. Service on these 90 minute flights is impeccable and I always feel that the flight attendants go the extra mile to make sure we gaijin are comfortable and enjoy the experience.

While I agree the Diamond lounge is not all that much, I confess I have a soft spot for it. I usually fly out of HND in the morning and it is entertaining to see folks star the day early with the draft beer machine.