[lugerholsterrepair]

Luke, It depends on what you mean by rough. Dents, scratches, scuffs, chemical burns, wrinkling, discoloration, peeling, cracking and some others that don't immediately come to mind. Post a photo on the Forum and I will look it over.
To answer your question, probably not much. Once leather goes forward it rarely goes back. Reversing damage, particularly to the outer surface layer, is rarely possible. There is considerable controversy concerning the treatment of vintage holsters.
Many people use various commercial liquids or pastes and the consensus is not to use those that have any petroleum base. Oils are bad in my opinion. NEVER use Neats Foot Oil. It is meant to break down leather fibers to break in shoe soles which will not last that long anyway.
Many holsters sent to me for repair have Pecard's on them and it is a sticky goo that I do not recommend. It is meant primarily as a water repellant on leather gear meant to be used in harsh weather and for that purpose I am sure it is the best. For vintage holsters I think it is the worst.
There is a line of thought that it is best to use nothing on vintage holsters and concentrate on ideal storage. I am a proponant of this theory to some extent. I think storage in a cool dark place with no pressure on the leather is going to help preserve your holster.
On new leather parts I make and dye, I use a product out of Great Britain that is sold in Jaguar and Rolls Royce dealerships for use on their leather automobile seats, Connoly's Hide Food. It seems to be a blend of Lanolin that is very gentle on leather, dries to a pleasant shine when buffed, has little darkening charecteristics and does not smell. It is not a panacea but from using many things over the years I think it does no harm and that is the most important consideration for me.
You mention value and
how treatment or repair will affect it. On some holsters there is no logical choice but to repair or replace parts. A holster with missing parts has little value anyway. Replacing them enhances value in my opinion if the replacement cannot be readily detected as a repair. If it looks original it is a good thing. The mistake I have seen here in my repair shop is shoe repair people getting ahold of a vintage holster . They tend to repair and not restore. They use the wrong thread and put holes where they cannot be taken out. Hope this helps, Jerry Burney