I'd go so far to say that Wash got enough development in the episode he decides he's jealous of Mal and has to spend time with him. I had been thinking while watching the series, 'well, what does he feel about the strong relationship his wife has with this other guy?' and that more or less answered that question. It also showcased how he could be more than a trifle obnoxious with his wounded pride but, predictably, put him in a spot and he both rises to the moment and wisecracks about it (would any Whedon character do different?)
Beyond that Wash didn't need
anything else - he was an affable, quick-witted character who wasn't exactly the most badass guy in the crew. We don't need his life story or his estranged parents or his elder brother he idolised or what have you; the snapshot we got I thought worked.
By contrast, we got
Travis' life story. And he's still
Book, however, would be a character I more liked as an idea but who wasn't that well developed or written (and often got some choicely bad
lines, like the one about the special hell - when that episode first aired there were pages and pages on this forum dedicated to people arguing about that line, good times.)
It was hopelessly vague, also, as to what sorta Christian denomination he was in. It's one that has celibacy for its 'shepherds' but in all other respects seems a loose form of Protestantism, which smells a little like the writers just mixing and matching whatever works. That character was definitely elevated by Ron Glass.