Lots of ideas about the same subject matter

I have Asperger's Syndrome, so I have a propensity for obsessing over a small number of subjects. Consequently most of my drawings and writings tend to share similar subject matter. Unfortunately my obsessive tendencies have not led to committing to any one project for very long. On the contrary, I'm bubbling with half-baked story ideas. I may get really excited about one idea for a limited period of time, but then I quickly burn out and either completely scrap it or at least put it on the backburner. This has prevented me from completing anything longer than a short story.

Why is it that I can obsess over the same subject matter for long periods of time, but don't apply this same obsessiveness to the stories which utilize these subjects? I feel like my major challenge is to arrange all my passions into one story that resonates with me. I know other aspies who have devoted themselves to the same creative project for years and I envy them more than anyone else. How do they pull their commitment off?