The breaker will be set against a mountainside, so will hopefully look balanced in scale with a large mountain adjacent. I'm really intrigued by The N Scale Architect's interlocking tower kits. I'm a tower fan, so will definitely have a few on my layout.
With an eye to economy, I adopted your idea in the form of a 1/2" Tall x 1/8" Thick x 24" piece of basswood with a scribed line down its length. I then fashioned posts of 1/8" Thick x 3/16" Wide strip stock so as to make the wall look more prototypical. I airbrushed it in a light white/gray, did a light weathering with chalks and glued it in place yesterday. I like how it turned out. My trainmen now have a safe place to walk and it provides some visual interest too. Its height is just above the embankment side, so it'll look legit holding back rip rap and I'll probably add some grass and weeds amongst the rock. None of that has been added. The black seen behind the wall is paint so as to hide any pink foam that may want to show in the side I cut away. Thanks again for everyone's ideas on this! I have other areas on the layout where I might use other methods.
I applied some scenic materials to the retaining wall embankment using some talus and bushes. I kinda envisioned the sort of rock and vegetation seen in the photo at the bottom. [Killian SC, 03/18/2016] It didn't quite turn out like in my picture, but I really like having the rock worked in there. The right-of-way will eventually have Kato ballast along the trackside.
Well sir, I'm impressed. That is looking great. The mix with the bushes, the rock, and the retaining wall is perfect!