We have been very happy with sources - it doesn't cover EVERY service we use (yet) but taking even just one or two out of in-house ETL is a huge benefit.
I would LOVE to see a Founders at Work 2.0 - so many incredible companies have been built since that book was published. The iPhone had just been released, for instance.
Steve was pretty explicit to Tim Cook and others that they should never ask "what would Steve do". He knew what that kind of attitude did to Disney after Walt died. It destroyed their creativity for years.
I think you should think about it as a multiple of what you would expect per-employee were the company to hire everyone off the street. So if you would get 10k options / employee off the street, what multiple of that is it worth to get the full team.