>going forward, referrer data would probably not be helpful for serious SEO.
I disagree. Keywords, gives us the intent of the searcher. It also goes to user experience. How can we possibly find longtail keywords, without this data?
How can we build Pages that fit the longtail keywords, without this data?
Longtail is about user experience. Google has extremely sophisticated methods to measure user experience, however, they're not sharing those with us.
I can see how people can become frustrated.
Even if you buy everything Google says, and you want to build the greatest website you can, Google is making it more difficult by taking away these tools.