I'm not so sure a scenic divider (in the sense of a large vertical wall) would be a good idea. There's very little space between the front and rear tracks in most places, so there'd be little left over for the back/right-side scene.
I'd be more inclined to go with disturbman's suggestion of mountain landscape, and use a grade to separate the front-left from the front-right (perhaps with some buildings or trees at the front of the layout to serve as a partial viewblock as well. You have nearly 10 feet of run between the two back-right track segments, so you could easily get 2-3 inches of vertical separation.
And you could do more if you put the upper line in a tunnel where it was close to the rear line on the right-hand side.
Actually, you could just use a tunnel without a grade to do that. I just dislike the "sheet of plywood" school of scenery.

Which is not to say I dislike flat layouts. Urban scenery in particular is often quite flat. And Japanese table-top layouts where the scenery is implied more than actual can look quite good. But if you're going to all the bother of doing real scenery, it's something of a cop-out to leave it flat as a board, unless you're modeling Iowa.