This is fantastic. To help other googling sketchup users:

painting rotation from one texture to another
copying texture properties
copy texture position

one method I have used for this is to copy the whole terrain down by the height of your curb then to create a block from the extrusion of your roads and intersect it with the whole model. after that clean up the model and you will have curbs and roads at a lower level than sidewalks. there is some work involved in it but it works.

I usually use the component spray plugin to place my tree randomly it has an option for random rotation wich is very useful you can have a look here :

http://forums.sketchucation.com/viewtopic.php?f=323&t=11746

have a nice day 😉

there might actually be a better or more proper way to do this but here's how i do it.

go to 'list' then new.. (and i guess you could skip this step if you want to add the texture to an existing list.. i put all of my created textures in my personal list)
screen 2.jpg

i've named my list 'scf example'... with the brush tool active, hold down command and the cursor will turn into an eyedropper.. sample the new texture with the eyedropper and it will show up like:
screen 3.jpg

drag the texture from the sample window into the palette..
screen 4.jpg

upon quitting SU, the .skm will be created and available for future sessions.

Would be great to have this functionality in Layout as well.