In the end, Lucky's argument, combined with additional research, was the most persuassive. I called UA and found that for the outbound, they had sold 5 C seats and there were 2 people on the upgrade waitlist. For the return, they had sold 9 seats (or maybe it was 11 - I've already forgotten) and there were 5 1Ks on the waitlist. Saving over $4,000 with those odds just seemed like the right thing to do. Of course, if it doesn't clear, I may end up spending more than that apologizing to my wife...