Yes in a few years you would be able to generate a complete avatar of someone, but it isn't them, and i think it will mess with you mentally.
But yes, it would be weird to generate more stuff spoken by your father by using this technology. And beyond that, what's even the point? It's not your dad.
I happen to be someone who believes that it's wonderful your dad left you with this artifact. It was a touching sentiment then, and now it can serve his obvious purpose many times over.
He didn't record himself as a side-effect of disease, or because he loved that particular story in the sound of his voice. He wanted people in the future to be able to hear what he sounded like!
Given that he could not have foreseen voice cloning (and therefore not explicitly asked for it) I cannot think of a more obvious example of someone wanting their voice to survive them.
I wish more folks would record The Night Before Christmas.