"The value of a painting depends on its state of preservation!"
When one considers the value of a work of art, one thinks at first of the price that it could bring on the market.
However, apart from the monetary value, the artistic and historical, and above all the emotional value, play an important role.
A timely conservation and/or restoration preserves value in every case. Furthermore, a restoration can confirm the authenticity of a painting and reveal the original intention of the artist.
For details in conservation/restoration measures, see:
Removal of Old Overpaint and Varnish Removal