Okay, I made the dirty track overlay again, I think it's quite good now. The texture is darker and seems rather like mud.
I made the catwalks at the top of the lift hill. They may seem very high compared to the tracks in the left hand bottom corner picture but that's actually because they're quite far of them (because of the width of the train). I also added the ladders to get to the top.
I think I'm ready to release this, or at least it will be very soon.