Many, I mean MANY, years ago my wife and I used United miles to fly from Chicago to Hawaii in First class (yes, I used to fly a lot for business on United) and when we arrived at O’Hare the curbside baggage valet told us that there had been a change of equipment and, since the replacement plane was smaller, we probably wouldn’t be in First Class.
Sure enough, when we got to the gate, the agent confirmed that we no longer had First Class seating. When I demanded that I be refunded the additional miles I had burned to be able to fly in First Class, she said that she couldn’t do that but to please accept $1,000 (probably $4,000 in today’s money) in travel vouchers to just get on the plane, PLEASE!
We looked at each other, accepted and thereby paid our next Hawaiian vacation the following year.
I don’t fly as much any longer but use credit cards to accumulate miles as most people do nowadays.
Also, when I used to fly for business, I would regularly volunteer to be bumped on my return home flights and received MANY free tickets as a result.