Ty - I've repaired numerous boxes of my own. I did it because the corners were busted and they looked bad with tape holding them together.
I use a citrus product called "Goo Gone" that will remove old adheasives and not harm the cardboard.
The metal corners can be cleaned up and recrimped with a little super glue behind them to hold corners of cardboard again.
I usually take an old shirt box (thin cardboard) and make a reinforcing inner corner in addition to the metal corner repair.
I enjoy having a box that fuctions properly for storage and in comparison to the previous looks of the box, I'm happy with the outcome.
Like refinishes, restorations, and modifications to a gun or antique furiture, many "purist" collectors will avoid any changes to an older/rare item and leave as-is (damaged state).
I'm a simple collector with a simple taste. I get pleasure from making junker things look nice again