To restore or not restore old photos? Spitfire RB140.

To digitally restore or not restore old photos?
I suppose like all restorations it becomes necessary to decide just how far to go with the process. In a small way the same must be true with restoring old photos.
How far should one go to improve an image without loosing the historic quality? Personally I concentrate on removing and repairing physical damage, but sometimes stop the process when tackling those scratches and printing disfigurements that could be regarded as part of the character of the photo.
Given the opportunity, sometimes exposure enhancement can lead to new discoveries of once hidden information that was locked within the photo, but again I try to avoid brightening the image too much, so that it does not look like a new print.
The differences can perhaps be seen by comparing the photo of Spitfire RB140 below, left in almost it’s original state, with the photo of Spitfire MB882 ( as seen on thread 75722. 6/11/07) which has been lightened to reveal more of the background detail.
Would anyone like to chip in with their views and experiences? FH.

What I have managed to discover so far –
SPITFIRE MK XIV. RB140
This is one of a series of photos profiling the Spitfire MK XIV. They were taken at RAF Friston on July 3rd 1944. Hand written notes in the P file at IWM state that the Spitfire MK XIV was still on the secret list when these pictures were taken.They were finally released on September 14th 1944.
The photographer was Charles Brown and the unit 610 squadron. This particular photo was taken only a few miles away from the airfield. Spitfire RB140 was flying west along and over the South Downs Way towards Alfriston in East Sussex. RAF Friston, a grass airfield, was situated very close to the famous Seven Sisters Cliffs on the hill between Seaford and Beachy Head near Eastbourne. It was the nearest airfield to this side of the channel, and therefore during the Battle of Britain and later, was mainly used for emergency landings. But as the war developed it took on a greater role especially during the invasion of Europe on D-Day. At it’s maximum the station had a compliment of 1,400 staff, mostly living in tents. many types of planes used the base, but in 1944 the Spitfires based there, accounted for many dozens of V1 flying bombs. It closed in 1946. Today, very little evidence survives of this front line RAF station.