It was me that bought an upgrade IAD BOG.
I didn't go to the airport aiming to buy it, but...
a) I was on the final leg of BOG SAL IAD FRA AMS LGW AMS FRA IAD BOG and I didn't fancy 5 hours in the back.
b) I was in possession of +100 space available e-upgrade coupons, my fare/route was valid and I had legally requested the upgrade and applied 2 coupons via the call centre.
After 30 mins discussing how their IT is crap it was confirmed that I had applied the coupons correctly, there was space available, their system did not work.
I half bought the upgrade to prove that there was indeed space available and I subsequently complained to Colombia's Superintendencia Financiera about Citi's bogus marketing (i.e. offering fake/useless e-coupons as a benefit of their LifeMiles credit card)
Was it worth it?
Actually it was a fairly reasonable expense. Like I said it was a 5 hour flight, it was also a bit bumpy and it was nice having space to stretch out and plenty of food and drink. I also did not pay for my ticket in the first place. Looking at the difference between return Y and J fares between BOG and IAD it seems to be US$1300 more expensive in J, so I didn't even get excessively gouged.
You don't get class of service bonus for a paid upgrade at the airport. Original booked ticket class applies.
I presume it is quite normal to offer paid upgrades, they certainly knew the process well. J cabin was full by the way. I don't know how many of us upgraded at the airport, maybe just me. And I don't know if availability of paid upgrades affects the price or if they are standard from point to point.