It turned out that in my case the message "The total price for your flight(s) is not available" was a red flag after all. That message in combination with an oddity in my after-the-call email confirmation (described below) caused me to call in to make certain that the schedule changes had been processed correctly by the first rep I spoke with.

When I called back the 2nd rep said that due to the fact that I had used gold guest upgrade certs on both flights the tickets needed to be reissued. She said that there was no rush but that the tickets would need to be reissued before the flight. After she got that done the new confirmation email looked right and the pricing info was back on the My Trips itinerary. She confirmed that if she hadn't reissued the tickets it might have prevented me from using online checkin. Apparently the reissue only needed to be done because I'd used the upgrade certs. If I'd booked in coach and stayed there (not a pleasant thought ) the reissue wouldn't have been necessary for such a minor schedule change.

The confirmation email oddity: Normally when I upgrade a flight at time of purchase the confirmation email shows me in class U. This was true when I originally purchased these tickets. But the confirmation email sent to me by the first rep after she processed the schedule change showed me in class K, the original booking class before the upgrade. The email sent by the 2nd rep after she reissued the tickets shows me in U again.