Don't mean to be bursting any bubbles here, but I don't think it quite works the way you've got it calculated.

I checked for myself as (i) I love Japan and (ii) I love miles and mileage runs.

The problems I had were:

(i) The promotion rules that I have say that you get up to 15,000 bonus miles for F/J and up to 7,500 for Economy (both round-trip). Is there an actual "double miles" promotion that I don't have or is this what you're referring to.

(ii) If I have the right promotion then I believe the cheap fare you quoted (I found similar out of NY) is a 'Q' fare, which is expressely excluded from the promotion.

(iii) Don't know if you would do it in coach, but if you're planning on upgrading (as I will most likely), don't forget to include the $500 cost.