Homer's dad embracing his son and his dreams represented the final act that had proven Homer's validity.  Winning the Science Fair competition, meeting his inspiration, proving to everyone in the town that his dream had merit all seemed to be a distant second to his father attending the last rocket deployment, and detonating the rocket for flight.  As the rocket is in the air, Homer's father stands amazed at the sight and embraces his son in a manner that reflects a father's love and admiration for his son.  The reader gets the impression that for the first time, the father is able to feel and show appreciation for his son. This is something that had not been fully experienced until that moment.