If the appearance of the scuff bothers, a Sharpie, brown crayon, small bit of black shoe polish would disguise it. I just ride mine as is. You're not wearing white right? You've already applied Proofide so I would take it for a ride. It may be perfectly comfortable as is and could be why it has never been tensioned any further.
Whether you do the bottom is up to you, but you might find it nigh impossible to get into the furthest nooks and crannies without drowning your saddle in the stuff.
What I want to know is what year Raliegh you have. I believe older saddles don't have date stamps on their cantles and I have an old cantle with the same saddle bag eyelets as yours and don't know what years these were used.