A Damaged Guitar

Greetings and blessings. A few days ago, I asked the Rabbi about a guitar I had that a friend of mine broke, and what the law is. The answer was: Even if the guitar can still be used, the one who caused the damage needs to pay for the decrease in the guitar's quality. This is estimated based on the value of the guitar before and after the damage. My question is 1. The guitar still has monetary value, but for my personal enjoyment, the guitar is worthless 2. It's impossible to know the value of the guitar after the damage.

Shalom!
Damage that is only emotional does not need to be compensated. [For example, if a person damaged a new car, and then repaired the damage completely, but the owner's enjoyment of the car is gone because it is no longer 'new'.]
If there is a decrease in the quality of the instrument, I assume that professional music stores would be able to tell you how many percentage points of the original value are gone as a result of the damage.