I just flew that route about a week ago. It was on an economy ticket. ICN-JFK I flew in Y with the seat next to me blocked. I didn't mind the 14 hour flight in economy, but then I'm used to so much flying anyways. Service was good as it always is on OZ, well good for economy, which is never going to be equal to C.

I spend an hour on the ground at JFK and then got right back on the same plane and came back to ICN. Yep, almost 30 hours straight on the plane with just the one hour break. But I got an op-up to C on the return, which was much appreciated, being the flight was full so there would not have been any way to block the seat next to me in economy. C was also full but I had an aisle seat. I slept for over 8 hours of the return flight, and the seat was comfortable enough for me and I wasn't disturbed by the FA's, other passengers, etc. The entertainment system isn't the greatest, but much better in C with the much larger screen I ended up watching 2 movies to pass the remainder of the time. In economy the screens are so small that I dislike watching movies there. Though actually I'm not really big on IFE in any class, regardless of how good it is. Obviously the service in C was much better, and the food as well.

Personally, I would never pay several thousands out of my own pocket to upgrade on this flight. But it's really hard to make a suggestion to someone else regarding it's worth, because everyone has a difference in their comfort level in economy, and difference in how much a few thousand dollars is worth to them.

I spent considerable time on the outbound just walking around the plane, chatting with one of the FA's, standing near the galley and looking out the window occasionally. I love flying and it was still a pleasant experience for me even in economy. If I was stuck in a middle seat for the whole flight though, it wouldn't have been so pleasant.