and i agree almost completely with your conclusion. he travelled for a month to clear his head, but returned feeling exactly the same. then he slept with reiko, whom was clothed in naoko's attire, and possessed the same physique as her. and he slept with her 4 times (which apparently is the japanese numeric equivalent of 13, and symbolic of death). he was essentially saying goodbye to naoko in a morally questionnable manner. then reiko and he parted, with the knowledge they would probably never meet again.

then we come to the last paragraph... i just don't see it as quite so optimistic as yourself! he's trying to move on - pull himself up from the inner world in which naoko was trapped (reference to "the well" also), but he's doing it too quickly. he's in limbo (the "place that was no place"), caught between the dark well and the life-affirming rooftop of midori, as you so aptly described. everyone is a blur around him. i see this moment as the same as when he returned from his month-long trip. he went away / slept with reiko to gain perspective and say goodbye, however, he still hasn't managed it.

the importance of this scene, and the optimism one can derive therefrom, is that he is CALLING OUT to midori to save him. naoko never sought to be heard (remember the night they had sex - she was talking seemingly to herself), but midori (part of life), always wishes to be heard and responded to. that is the optimism, that is him wanting to reach out as you describe.

so, essentially, it is uplifting, but that last paragraph is as hopeless and melancholic as the rest of the book. what a truly wonderful read.

and sorry for rambling so much - didn't mean to!

- chris