This looks great. If like this example you want to do watercolor style images then I don’t think you need a renderer as the styles are better accomplished in photoshop. Maybe you do this already, but exporting separate Sketchup layers can be a better way to control discrete elements once in photoshop. For example, output only what’s behind the wall as one png image, then output just the wall as another, and finally output the elements in front of the wall, maybe the tree is separate too. then in photoshop you can work on them separately and once you have a final comp it can be falttened and then blended?
If, on the other hand you want “photorealistic” images, then a renderer would be appropriate.