Isn't there a saying that states you end up marrying someone who's like one of your parents? I might be misstating it, but I'm pretty sure that's what it is xD.
But yeah, I never really did understand Ginny and Harry's relationship either. I knew he was developing a crush toward her at least in the fifth book (might've been earlier), but for whatever reason I dunno. I do remember that Ron was very weirded out by it, though. Probably because they were best friends, he wasn't as overprotective of Ginny when it came to Harry unlike other boys she was dating with (like the aforementioned Dean, completely forgot about him xD).
I just remembered that in the books, I do recall seeing a hint of Ron having a crush on Hermione in the fourth book when she was going out with Viktor Krum. It was most noticeable with the Yule Ball chapter, though it was covered up with the infatuation with Fleur, so... yeah.
I think that the parent thing might be more personality than looks, but then Harry couldn't choose someone like his mum as he never knew her, and it doesn't really work in the same way when you're told about it.
I never noticed a developing crush towards her in the fifth book. They could talk to each other by then, but that's about it.
Yeah, Ron did have a little crush on Hermione in the fourth book, though it's beyond me why she returned his feelings. I know that opposites can attract, but they really are just too different IMO.
To be honest, I think that the first four books are my favourites, the fifth one I am pretty much indifferent to (though I can't read it without getting very angry on Harry's part as literally everyone lets him down multiple times and seemingly just expect him to be okay with it), the sixth and seventh, I just don't know. In those ones it seemed like all the progression the characters had made, Harry and Hermione in particular, just ground to a halt.