> - The primary effect (as far as I can tell) was in convincing all the executives at Apple of the value of the GUI.

That's my takeaway as well. Larry Tesler says as much somewhere.

I'm not sure about the talent thing. The overall vision for the Mac as a shipping product came from Steve Jobs, who was never really an engineer. The original Mac team members have been very clear on this point. The engineers, however talented and visionary, necessarily had smaller scope (which is why they were engineers and not executives).