For those who have a fair amount of familiarity with Premium Plus booking and price fluctuations:

We've never flown in PP before, but were considering the buyup for an outbound flight IAD-LIS in April, and again outbound IAD-BCN in September. Currently in 32 K/L "preferred seating" thanks to my lowly Silver Premier status. (FYI, all flights are nonstop 767-400ER.)

As luck would have it, just before I was going to pull the trigger on the LIS flight, the buyup price jumped from $375 to $847. Not a price I would consider. There are still 16 of the 24 seats available, and I believe that number has been constant since the price increase at the end of December.

On the BCN flight PP is completely empty. The buyup is $375.

Anyone here have any experience with price fluctuation in PP buyups well in advance of the flight? I very much would like to see the cost of the LIS upgrade come down before I would consider buying the upgrade. But I'm also curious whether the $375 buyup for BCN is pretty much the floor? If the flight goes another few months with no takers might the price drop further?

Final buyup question: Does what was paid for the flight have any bearing on the cost and/or opportunity for the upgrade? The IAD-LIS flight was a really cheap $529 in S class. For Spain, the IAD-BCN flight was 40K miles and booked into XN class. The return from MAD-IAD at the beginning of October was 30K miles, also in XN class. Even though that flight is almost empty, UA won't offer me any upgrades in either Polaris or PP. "This reservation is not eligible to be upgraded."

TIA for any insights you might have.