Saying you don't get value from social media is a little like saying you don't get value from writing a letter to a friend, receiving a postcard from a distant relative or a phonecall with your mom. You are confusing the medium with the message. Online Social Media is just a channel for communication. You can talk about your life, your experiences, make real connections, share new ideas and be connected in surprising ways. Or you can just post photos of cats. What makes any channel of communication work for you is how you use it.
Social media for a design firm shouldn't focus on pushing out your message (social marketing). Instead focus on building community and conversations with clients, the industry and with society. Check out http://gapingvoid.com/