Looking for tips on restoring vintage photo that showing wear

The attached scan is of a postcard from early in the 20th Century. The postcard was never used, but it shows a cloudiness on the surface that appears to be wear. I have tried several different ways to minimize the appearance, but nothing has improved the image much. I've tried:

1. with curves layer -- adding contrast (increase contrast, medium contrast, high contrast, linear contrast)
2. with curves layer -- multiply
3. neural filter: "photo restore" -- at 25%, 50%, and 75%, but very little improvement 
4. neural filter: "Jpeg artifacts removal" -- High, Medium, and Low
5. Whole image vs selection -- I've applied these four steps to the entire image and two a section of just the affected area (largely the right side) and adjusting transparency, but no significant improvement either way. 

Has anyone found a tool or tools that can iminize the "wear" or abrasion showing on this photo?

Thank you!