I've been PM for a few years now and still haven't mastered the "RUC game". I live in SEA and often fly to destinations in the upper Midwest with connections at either MSP or DTW. Those legs between SEA and either MSP or DTW are tough upgrades because they connect hubs and hence there is a lot of competition from other elites.

I haven't had a complimentary upgrade to F on SEA-DTW/MSP in years. Sometimes the "first class monetization" offer to upgrade is relatively "cheap", like ~14,000 miles. In those cases I might opt for such an upgrade on miles instead of burning a RUC. I usually reserve the RUCs for when I take the SEA-MSP or SEA-DTW "red eye", where I really place value on an F seat.

Really, I think the best you can do is monitor the seat map to see how the C+ and F cabins are filling, and how much they are charging for cash/ mileage upgrades. And apply a little common sense . . . Monday morning and Thursday afternoon/ evening is always going to be a tougher upgrade than a Saturday.

At the gate, it can be interesting to see if they utilize the "Diamond" boarding group and if so, how many board. If all Diamonds have been upgraded, then there is no need to call the "Diamond" boarding group, and I have seen several flights recently where they skip the Diamond boarding group. If some Diamonds board during the Diamond boarding group, that may be an indication that no PMs got complimentary upgrades (I know it is not a foolproof system, but it can be indicative and informative).