I didn't even know the GT Premiums had ambient lighting until after I brought mine home
My first night driving was a pleasant surprise. But honestly, I think my friends are more excited about the lighting than I am. It's pretty cool, but at the same time, I can live without it. I bought the car mainly for its performance, after all.
Oh, and as far as brightness is concerned, you can adjust it, and can even turn it off completely if you want to.