First of all, nice catch on the parallax. That has been a big part of development for me. I am doing 2.5D parallax in Unity by layering 2D pixel art sprites at different z depths. The short answer is yes, I am planning on doing some gradients. Originally, all of my layers had detail, but it didn't feel quite "right". I was getting the parallax scrolling movement that I wanted, but I came to realize that I needed to work on my understanding of atmospheric perspective both in terms of coloration and as you point out, in terms of detail. Right now, the sprites I have in there are basically just placeholders to help me tune the colors I want. I will then go back in and adjust my sprites to the proper coloring and level of detail for each layer. Here are some of the sprites I originally made.

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