When you are at the routing stage, only changes are visual. And looking at the text comparison of two different version of a .kicad_pcb file isn’t really helpful for this.
It would be great if there was tool that can correctly display/highlight changed parts of two different version of a pcb file. But easiest method is the image comparison method as this guy did: http://www.evilmadscientist.com/2011/improving-open-source-hardware-visual-diffs/ or this one: https://github.com/hurik/JGeagle .