I would leave well enough alone.

Need a panoramic view to see one side -- the most important view -- all at once. Use the pano feature of camera or take in slightly overlapping pictures while you STAND AT ONE SPOT and pivot the camera.

BTW, if you walk away ad do nothing, you'll automatically end up with a "natural solution."

It's nice to hear the "do nothing" solutions! I just have a couple concerns with that.

1. I can't just leave the grass growing there, as I could get fined. And I don't want to be stuck constantly trimming the hard to reach places on the slope.
2. Erosion. Should I be worried about the trees?
3. Nature/weeds taking over the lawn.

Was just pointing out that when weeds and nature take over, that's a 'NATURALISTIC' solution (as you said in your introduction that you preferred.) :-)

See if you live in a area where hydroseeding Lespedeza would work for you. (If it's a large hill.) I don't think anyone knows where you are.