I had success this September, from SIN to PVG one way, on a full Y fare. Upgraded into the regional business class (the seat was still very nice, on par with many international J seats). It was TOTALLY worth it (only 15,000 miles... fare difference was nearly $2000, I think).

The only problem is that you can't waitlist. I made it part of my morning ritual for two weeks: get up, eat breakfast, check for an upgrade. I think there was finally space available a week or so before the flight. Interestingly, the flight sold out a couple of days later and you couldn't even buy a J seat.