I think we all have similar problem. For some of the projects I use very high quality grass texture with height, reflection and ao maps.
If you want to have it in 3D geometry I would paint only area right in front of camera. It really depends on camera’s scenes. Usually I use two materials in sketchup (first for grass that is far away and the second one for close ups grass). Then it is easy to paint those areas with bucket tool. Also I do it as a last step due to performance issues.
Anyway it would be cool to have scattered grass as a layer to turn it off while working on file. For now you have to use eraser tool. You can of course use standard paint tool.
Furthermore it would be great to have similiar tools for grass as it is in lumion.
For now we have to do some workarounds.