When to restore?

[B. Dudley]

As you said, a search of old threads will yield some answers to your question because it has been asked here a number of times before.

I will lend some thoughts here now.
You restore a gun mostly due to lack of original condition, combined with your desire for a gun to look like new or at least newer than it does now.
Some "restoration" such as barrel bluing can be looked at more as maintenance.
Re-casing a gun is never nessecary from a functional standpoint and, in my opinion, is the last thing to be done when it comes to restoration work. It is the final piece of the equation next to barrels and wood.
Restoring a lower grade gun is nearly always a labor of love with no financial benefit unless it is in a rare gauge or configuration.