Y is way oversold on that flight, and C is wide open. So there is a good chance for some op-ups, I just don't know if it will be you. I'd use the miles.

Funny, I was in almost the exact same position a few days on a flight to NRT (2P status, maximally overbooked Y, empty C), except that I didn't have the option to use miles. I waited and listened for my name to be called for a free upgrade, but it never happened. Maybe there were a lot of misconnects/no-shows or too many 1Ks waiting in line ahead of me. I'd love to know why, but of course I never will.

I wish I had followed GRE's wise advice: "Never even think about an op-up. An op-up is a completely unexpected gift."