@Hook: You've got a good start here. Keep practicing so that you can play the whole thing smoothly without starting over and you will have a pretty nice arrangement. Simple and sweet, which is what a "toned down" version should probably be.
I have thought about how to do this for a while. I have come up with something, but don't have a whole lot of experience working with my electronic music production software (Garage Band, which is not really that fancy anyway), which is probably what I would need to use in order to make it sound halfway decent (I'm generally more of an acoustic musician and composer). I could try my hand with sequencing something in my notation software, but that probably wouldn't be as good since notation software is made for notation rather than sequencing. Go figure. Anyway, if I do ever put something together, I'll definitely share it here. In my head, it sounds pretty cool. The trick is, of course, whether or not I can translate what's in my head onto another medium that other people can hear, too.
I have something envisioned like one of the remixed versions of the Cave Story 3D theme that Nicalis had on its website for a while (maybe it's still there? I don't know). There's an extended video of it (along with one of my favorite works of CS fanart)
here.