One of my aforementioned friends e-mailed today to say he'd gone through the book and totalled his career at 2,355 Doak points.
So I just went through it and came up with 2,677 for myself. There are still a lot of courses I didn't play, so there must be between 3,500 and 4,000 total points in the book. So there's a target for everyone to shoot for.
However, I suspect the more courses you've seen (especially the best ones), the less important it becomes to play a course in order to visualize what's going on.