Generally a few billion dollars, Daniel Gross says, in a short Slate piece:
The real alchemy of finance is to endow those skilled at finance to wield authority in adjacent or even unrelated areas. That's the general theory of Davos, bankers sharing their theories about nonbanking subjects. Stick around and you'll hear a lot of conventional wisdom on globalization, climate change, poverty reduction, financial crisis, but it somehow sounds deeper and more weighty because it's delivered by an extraordinarily wealthy CEO, a private equity executive, or hedge fund manager rather than by a journalist.
His case-in-point is George Soros, who we listen to on topics ranging from U.S. politics to philosophy, even though his views in these areas may not be unusually insightful.
The truth is we listen to rich people on a range of issues not for their insights but because a billionaire is in a position to actually implement the conventional wisdom. Is Bill Gates the most original voice on education reform in America? No, but whatever he does believe, banal or not, matters, because if he wants to make a difference he can.
Still, Gross's point is well taken: expertise is context-specific, and billionaires rarely have the most interesting things to say.