So I've just noticed that BMW and Mercedes have this metallic color paint for their exterior and they differentiate their metallic paint with non metallic where they charge extra amount.

Lexus IS has the silver lining metallic paint, but that is it.

Is metallic paint suppose to be more valuable and luxurious?

 

I don't know about value and luxuriousness. But it certainly gives the vehicle a different look. Everyone loves something that sparkles! I would imagine the paint costs more. I think several manufacturers other than BMW charge extra for metallic paint.

 

Pretty much all manufatctures charges extra for metallic paint.

On the lexus, the only color that are not metallic is the black.
Every other color is metallic, even if it is not part of the name the paint has.
And yes, you do pay for the extra look. And metallic paint always comes with a clear coat on top, making this kind of paint more durable.
Normal non metallic paint are in some cases just a basecoat without a clear coat. But these days, most non metallic paints also have a clear coat on top.