Over in the UK we have a programme called the Antiques roadshow. Family heirlooms are presented and an expert examines them, gives a potted history and suggests a valuation. All fascinating stuff.
But when it comes to furniture and one or two other items - then the patina - ie the shine and colour developed over the years is to be retained and is perceived to be confirmation of the age of the item.
I would perhaps wipe the saddle with a moist soapy sponge to get the surface dirt off but otherwise I'd leave it - perhaps as a memory of all those folks who have sat on it.
I would be more worried about whether the saddle fitted the horse.