Dave, the father figure feels somewhat like like a misdirection, no? If this was a more conventional movie, I would say he is being set up as the "good motive, extremist, turn into bad guy" role early in the film. But it turns out he is not so extreme as to want the planet's destruction, and is a caring father. I think his "function" in the movie is to provide a backdrop to Ponyo's fantasy elements. Though I appreciate JediFonger's perspective on cultural differences in the review thread, I tend to think sometimes we overstate the mysticism of the East. With Ponyo being a central character in the movie, Miyazaki has to provide some kind of background to explain her powers and transformation, and the father is an entry to that world. I would not be surprised if the filmmakers had an elaborate backstory for the father and mother, but ultimately the story is about the adventure of the two kids. Perhaps by making his character more simple, or by giving him a lot more screentime, his character would be more satisfying.
To me, that may be part of the charm of the Miyazaki films. The Pixar movies, which I also love, comparatively have perfectly thought through threads. If something is mentioned early in the film, you know it will come back and be resolved later in the film, including its planting of the villains. I find that immensely satisfying. But the recent Miyazaki films seem to give me the moment-to-moment surprise highs more, even if I feel the overall story isn't as completely told.
I don't think this shows a lack of storytelling ability on Miyazaki's part. Naussica, Totoro, Kiki, Porco Rosso and so on showed Miyazaki perfectly capable of telling stories without hanging threads, even enormously large scale stories such as Naussica and Castle in the Sky. Like other filmmakers that put different emphasis in different times of their career--David Lean the editor vs. the cinematographer, Kubrick pre and post 2001, the dynamic Kurosawa and the more contemplative one--I think Miyazaki now prefers to throw us in a big, magical world and just go with it. I recall in the HTF discussion of Spirited Away, someone wondered why the girl got a chance to save her parents at that particular moment, and my view was just that Miyazaki had given us enough of a ride, that it was time to end the movie. Not a particular deep reading of a film, I realize, but I thought any conventional character "growth" or "journey" in the Joseph Campbell sense could have been too easy to supply at any moment to end the movie anyways.
Re: English dub: I don't know if Disney released Ponyo with its Japanese language track anywhere in the US. They did in select theaters for Spirited Away and Howl's Moving Castle. I saw both of those movies in Japanese first. Like with the Ponyo English dub, I find the English tracks to be perfectly fine, but still feel the Japanese voices to be more expressive, especially in the more extreme emotions.