First up, be sure never to think of airline upgrades the way most travelers think of them: good fortune bestowed by benevolent check-in staff or cabin crew.
Here’s a quick upgrade heads-up:
An upgrade is something bestowed on you, but not by the airline. By you.
The penultimate upgrade is coach to Business for not much more than the price of coach, or for same price as coach, or even less than coach.
The ultimate upgrade—coach to First Class. Again… for not much more than the price of coach, or (rarely) for same price as coach, or (even more rarely, but not unknown) less than coach.
Each can be achieved through various strategies First Class Flyer invented or perfected over the last 20 years, or just by little-known (unadvertised) flash sales.
And there’s the upgrading of one’s own mood, maybe even esteem. When you get to choose between two different prices for a premium airline ticket, one extravagant and the other extremely reasonable, the choice you make affects the spirits.