NEEDHAM Since 2010, Boston Brunchers has grown from an informal group of scribes meeting monthly over the most leisurely meal of the week, to a 150-member powerhouse that’s become one of the most influential groups in town. So much so, that restaurants comp their meals, hoping for a positive blog or tweet. In a rapidly changing media landscape, where restaurateurs and others in the food industry struggle to compete, inviting citizen reviewers in for a gratis feed is an instant way to fuel one’s social media cred. Many of these bloggers are recent college grads who can lure the elusive 18-to-34-year-old demographic to patronize these businesses.