Wrong place to get a Star trek reference wrong....

Star Trek doesn't have paygrades because Star Trek doesn't have money. Try the U.S. military, the stereotype of the corrupt commissioned officer saying things like "Askin' questions like that is above your paygrade, son."

I think that is probably more literal than a person should be with a simile, metaphor or poetical comparison

The phrase was used in the last episode of The Orville, I think we should accept that into cannon and ignore everything JJ Abrams has done.

Aside from that, Star Trek has Latinum bars and Credits as the plot dictates.

I never heard it from that perspective - only from below, as in "I'm not paid to worry about such things". (And/or implied not qualified, which is how I read my OP-ish.)