Redirecting attention to important things?

What would be the phrase to use in case somebody complains about minor fluff while most important thing is in place? In Russian you would use "Вам шашечки или ехать?" which literally means "Do you want a cab sign (or lights) or do you want a taxi?".

Thanks!

Farid.

I will go with, Is it fashion or function that you're after?

If I'm understanding you correctly, someone is concerned over a minor problem. One idiom to rebuke such a person is Don't sweat the small stuff.

[S]omething that you say in order to tell someone not to worry about things that are not important. - TFD

If a person worries about trifles while failing to appreciate the big stuff already in place, you can say they can't see the forest for the trees.

Focus only on small details and fail to understand larger plans or principles

(TFD)

In certain contexts, penny wise and pound foolish could work:

Overcareful about trivial things and undercareful about important ones.

(The Phrase Finder)

Another colloquial idiom for a person who has their priorities wrong would be majoring in the minors.

You could say, "Don't major in the minors!" to get the message across.

You could consider saying, "You are not looking at the big picture." The big picture means:

the most important facts about a situation and the effects of that situation on other things

"When you look at the big picture, a slight increase in unemployment is not significant."

[Cambridge Idioms Dictionary, 2nd ed., Cambridge Dictionary of American Idioms]