That's a great price. Whenever I flew round trip to the US then I would book economy on UA and upgrade using systemwides. I never even shopped JAL/AA.
I would stick with OW if I were you.
A "full fare" economy on UA trip last year to upstate NY from TYO was $4300. The business fares were $7k I think so I couldn't justify that. So I used that money to buy an economy RTW ticket instead (like $100 more) where I upgraded all the longhaul legs (including Lufthansa) and M class (RTW booking class) on UA automatically upgrades into F.
I've seen HND-SFO mid-week roundtrip for as little as 270K JPY. Not sure what booking class it was, but I think it was "I" -- non-refundable and all that badness. I think you only get this pricing if you book more than 3 weeks out.
I usually get my tickets in X with some fixed rate fare, and it's usually still 100K less than the competition (NH/UA) on that route.