Geoglyph is good, but not a magic solution. Most coloring macros just shade with solid colors. What you need is texturing either with shaders in houdini, or file textures in world machine. You can import rgb textures using "file input" device set to "interpret as RGB". I'll link an example of file based texturing right here in worldmachine.
1. Reduce size of trees to 3/4 the current size 2. Yes, add 1.5 times the current amount of trees 3. Use some better texturing on the slopes, looks like paper for now. For illustrative use this would have been good though. 4. I like the bridge idea, but doubtful if the shapes in your terrain will allow it.
For photorealism, terrain itself may need some more work. Also, what do you use to populate trees? Avoid populating on visible slopes. That's all I can think of at this point. I like your scene assembly though. A bit more fine tuning, and it will shine!
My goal is to get as photoreal as possible. I know adding more trees and vegetation will help, but I think I need to add a man-made landmark to really sell it, that's why I was thinking of a power line tower, but they are not very nice looking, my other option is to add a bridge...
This is my second post, I wanted to share some wip with my WM > Houdini pipeline. It took me me about 3 days to put it all together. Next I want to add more details and elements - maybe a power line tower crossing the terrain... I'm open to suggestions.