That's a tough one.
If you read what happened this really wasn't about the truck. This punk kid wanted to insult, affront and mock the OP. He did it, then told the kids friends he did it, told the OP he did it and when nothing happened then he did it again. The OP tried to do the right thing and reported it to police, dean was made aware etc...again nothing happened. It's easy to sit back and say the OP should've done this or that in hindsight, but think about what you would do with this punk up in your face, bragging to your friends and you about what he did,every day, and your just waiting for him to do it again knowing nothing will still happen.
I'm the guy that always broke up the fights but I'm not sure what I would've done.
I think you, the OP, may have been able to take him to small claims court and possibly recouped some of the money for the damages to your truck.
Makes me wonder what would've happened to this same punk if he was doing this to the Dean's car under the same circumstances, would the cops have said, "awe, shucks nothing we can do"?
that being said, I would never have advised my son to fight someone, unless it was to protect himself or someone else, neither would I admonish him for having done what the OP did.
Best of Luck to the OP!