I've always selected the max # of SWUs since the days of "choice." Never had a single one expire unused.

I generally buy tickets where upgrade space is available at time of booking. I occasionally have to roll the dice, and on such occasions, the upgrade has either cleared before day of departure, or on day of departure. Haven't sat in the back yet.

All the above is great. But on the negative side, YBM fares from SEA to Europe or TPAC are routinely in the $3-5k range. Ouch. That's taken a huge bite out of the value.