Well the point that is being made is that (or what I am taking from it) it may be better to leave as is.
So then I have to ask, what about a guy like Turnbull who does some amazing restoration work, what's he doing differently?
Others may take a different view of this but here's how I see it.
Enthusiasts often come at things from entirely different perspectives. Here's an example outside guns. If you are into high performance sports cars, the world sort of divides into two camps....those that appreciate and value the teutonic engineering of Porche and those that favour the beauty and passion inherent in marques like Ferrari and Jaguar. Both like sports cars but they have vastly different yardsticks.
When we are talking old SxS's there are two divergent approaches, both held by people who love these guns. For simplicity sake I'm going to call the first approach the English approach. That is that these guns are made to be used and enjoyed and to do so properly they must be maintained. Occasionally that maintenance might require some significant work if the condition has been allowed to slide.
Alternately there is what I think of as the American approach. That view holds that the most valuable examples are those that have not been used. Are "as new" as a result of sitting in a case, cupboard or safe for the last 100 years.
Now this is a vast oversimplification, but I think these two viewpoint are the starting points for the attitudes of just about everyone I have come into contact.
Turnbull has spent a lot of time, as have others, becoming expert is restorations. In fact he is so good that his work is sometimes viewed as acceptable by those who really are looking for NIB but have a gun that REQUIRES work, for one reason or other. As a result Turnbull can charge some pretty good prices.
But, in regards to these prices, remember, the processes involved in restoration are extremely time consuming and properly done by master craftsmen/artisans. Their time IS worth money and the quality work produced reflects their care and passion for what they are doing. Without meaning to denigrate others, that is different than the average gunsmith.
What sets Turnbull apart is the quality of the work and the quality of his brand name (the result of his work and self promotion). There are others who do equally good work but who are not household names in this community.