First law of Bryce is scale everything big...really very big! Then place them in your POV. This helps with the haze factor and gives a sense of depth. Secondly, always edit your textures in the DTE so that the colors are a wee darker than offered. In other words, tweak your textures to fit the situation and lighting. You may have to increase/decrease a texture's frequency in order to achieve a desired look and this may change on your sky layout and lighting. Also, it helps to turn off the Sun link in your image.