Technically my undying alleigance is to the guy who got crucified a little under two thousand years ago, because he told us to work for social justice, which he said was the best thing we could to to worship God.
Also from the book of Amos:
"Though you offer me your burnt offerings and your meat offerings, I will not accept them, neither will I regard the peace offerings of your fat beasts. Take away from me the noise of your songs, for I will not hear the melody of your viols. But let justice run down as waters, and righteousness as a mighty stream."
The context of that is the oppression and class discrimination that was rife in Israel at the time. Basically, you can worship all you want, but it's pointless if there is no justice in the world.
Well, we're not supposed to look at God as a prayer machine, who dispenses reward and punishment because of things we do. That's an old and flawed way of thinking.
Why pledge my undieing allegiance to a being that won't give me anything in return?
Because it doesn't exhaust any of my resources, which I can spend bettering the lot of the unfortunate, which is kinda the point.
But surely God could prevent it from upsetting natural order - he's supposed to be omnipotent, not a superhero from a comic book...
You're looking at the wrong definition of omnipotent though. Something that disrupts the natural order of a thing is "evil", because that's not how it's supposed to be (like, say, your hand getting cut off.) And god by definition won't be able to do evil, because god is pure act, act is by definition extant, and evil is by definition what is not.