Like you, I try to treat the stewards with respect as I'd like to be if I did their job.
Most of them are pleasant enough I've found but I have also come across some that just see it as some kind of strange power trip where they get off on the 'control' thing.
After a recent game I got talking to a very pleasant young lad who was a steward.
He was actually a City fan, but he did say that he knew a few United fans who worked The Etihad. This young lad said that the Stewards are treated better than at the Swamp as their welfare is considered more and apparently they are offered a drink and something to eat .
Having said this, they probably are still on minimum wage though as you say.