Do send out a newsletter when you have a new book out or are going on tour. Also list relevant event dates and notifications of contests you are running.
Don't send out a newsletter just to send out a newsletter. One newsletter a year that is really interesting is more beneficial than 12 that are boring. If you write two or three boring newsletters in a row, your readers will start to think you write boring books.
The most satisfying thrillers send ordinary people into battle against the forces of evil - otherwise known as greed, ego, rage, fear and laziness - and bring them out bloodied but whole.