"Tracks Ending At The Wall Dilemma"...
Years ago, during an experiment with 3-rail modeling, I faced just such a situation, but in my case it was a bridge also hiding a stage entrance as well as a wall.
I was going to mute the situation by painting the wall under the bridge black. Here's the mock up of the scene:
* Lower the height of your bridge so not so much of the wall is visible. (You can use cardboard for a mock up bridge like I did before you make irreversible changes to your current bridge model.)
* Place a section of black poster board against the wall to simulate a black-painted wall.
* Use some "Tacky-Tack" gum to temporarily hold some flats in place on the wall "past" the bridge.
Look at the results and see what you think.
In my estimation, adding mirrors to the wall (either the entire wall or just under the bridge) will draw visual attention to that area. In my opinion, that's not what you want. You do not want the scene to GRAB attention or compete for visual attention in any way, instead you want it blend-in as best it can and compliment the main scene.
Something to think about.