Reserve always paid off more than friendliness in professional life.
However, given the conversational tone and universal reach of social media and social networks, now being accessible has become a must in that professional persona. Although some passionate thought leaders may be tempted to be friendly, in a time of extreme over-communications that's not a smart move. Politicos should keep that in mind during Campaign 2016.
The lesson here is the same that Willy Loman should have learned in "Death of a Salesman." That's this: It takes lots more than glad-handing to sell, ranging from a point of view to products and services.
In a speech, for example, thought leaders do a bit of self-disclosure. They show (not tell) that they are open to input. They wrap up the address with contact information such as a Twitter handle. Afterwards they widely distribute the speech and invite media interviews.
But, the persona has to be framed as professional. There is no indication that you are Best Buddy. Instead you place yourself out there as a tool your constituencies can use to get what they need.