I have kept every HR ball that my son has hit that can reasonably be expected to be retrieved. My son still plays in MSBL and I have donated a box of baseballs in preseason to every team he has played on since his youth ball days......
I will say that this meant more to me than it did him. As I have an extensive collection. I also know he had raided this stash of baseballs to use in a Homerun Derby Contest in college.....so much for his attachment.