How to write in one draft

Pounding the mean streets of New Malden last night, I was thinking about why I do what I do when I'm writing a novel, and why it seems to work. 
Now I'm on my third book, The Method is reasonably well established, and boils down to this:
1. Do some world design and character development until it's rich enough that you can't bear not to start writing.  (1-2 weeks)
2. Write until you feel your ideas, which now feel thin, vacuous and trite, can no longer sustain the narrative.  this seems to be about 30,000 words; at my current rate about 10 weeks)
3.  Go back to design
a. Make a list of all your characters - including the new ones which have made bids for fame so far - restate their motivations, objectives and outcomes, and make an explicit list of all the scenes they will appear in - adding any scene detail as it occurs.
b. Put together a spreadsheet of all the scenes in sequence, using what you've written as a start, then add all the new scenes in the correct order.  Add columns for characters so you can see who is in which scene, and highlight the PoV character if appropriate.
(2-4 weeks)
4. Write the book scene by scene, referring to notes so you don;t miss all the cool detail and dialogue sound bites you thought of along the way.

So I started thinking this is like taking part in a play, and you're trying to understand the story and the characters.  First of all someone tells you a bit about it, and you get interested.  Then you read the actual script, just enough to get a feel for they style of the dialogue, the setting, and the characters.  Third I'm actually in the rehersals, trying to get everything perfect, until finally it's show time.

That's the plan.  Let's hope it will be all right on the night.