Through the good offices of Criterion Channel, I've been able to see this doc. I'd say Fancher's life was one of the more remarkable ones in Hollywood history: imagine starting out as a flamenco dancer, studying in Spain, then relocating to Hollywood where he carved out a precarious life as a bit player, then as if his natural laziness could find no other outlet, writing scripts. He is clear about his desire to shirk work; taking parts if they will only involve a day's work, and doing the least amount of writing possible. I doubt if very much of the Blade Runner script is by him--it would be interesting to compare his work with the finished film.
Fancher is digressive, endlessly so. The story of how he tried to collect a debt for Teri Garr seems to go on forever, with no punchline. He is entertaining sometimes, and the film clips, especially those from Parrish, are fun to watch.