We were upgraded when flying for FIL's funeral (LHR - JFK on BA).
As it was a funeral, we had booked just a few days before the flight, not getting any discount on the economy fare.
When we tried to bag-drop, the computer said no and directed us to a desk. DH assumed I had fluffed up the booking. The agent said, "I am pleased to inform you that you have been upgraded". That was for three of us, and I am still annoyed at DD for not using her lie back seat! It was such a lovely flight, contrasted by being in a narrow pipe for our connecting flight to the mid-west.
A few weeks ago, we were travelling to Toronto with Iceland Air, via Keflavik. We booked Saga class, which is the highest level of service Iceland Air has on short-haul flights (top service apart from the lie back seats). Whilst on the Tube from T5 to T3, I got a text telling me about our connection in Montreal. I thought, we are not going to Montreal, but I am not going to worry about it until we got the terminal. When we entered there was a message about our flight to KEF having a two hour delay, which would have scuppered our flight to Toronto, so they booked us on Air Canada. The AC flight was full business class - lie back seats, champagne and pampering.
Big shout out for Iceland Air. Their Saga class seats are less than half the cost of BA/AC with great lounges, fast-track, etc.