As has been mentioned before, the direction of track does not affect AI driving, but does indeed affect the placement of trackside objects. I have,also found that putting the track down in the intended direction of travel does help with junctions and curves as the track tends not to curve and bend oddly in those places when straightened.
When the track work is extremely complex, I have found fewer track markers as being the better solution along with placing them before, middle, and after complex junctions. The before mark gets the AI into position while the middle gets them into the middle of the route, and the exit gets them out of the route while anything more than that makes them extremely confused and prone to SPAD'ding as they speed up and slow down as they load up the track markers.