The ideas are the similar for long or short fiction, so useful for both. Personally, I find with my stories that I go in with some idea of plot but a lot of the plot is created organically. As the characters develop, as they come up against the conflict, as they interact with each other plot can grow out of that.
But as you say, the characters also develop interesting shades as we write them. Good luck with the longer fictions and thanks for leaving such a thoughtful comment :)