In my last 50 or so games probably, I've seen one, maybe two soraka. I actually thought the title was sarcasm at first.
Anyway, for what she brings to the table: Heals, poke, heals, an anti-assassin silence, and more heals. She is one of the best champs at stopping ability-centric assassins, since she can just put her silence field beneath the ADC when the assasin goes in, and the assassin is left dead in the water. Zed ults? Drop a silence field. Akali dashes in? Drop a silence field. Fizz being fizz? Drop a silence field. Her heal, when she builds AP/CDR, heals for a ton on an incredibly low CD, which can easily force wins when someone is being focused, keeping them alive long enough to put out the damage needed to kill the foe, while hitting with her Q keeps herself healthy. Her ult is one of the few global ults in the game, and allows her to impact both top and mid lane during lane phase without ever leaving her ADC's side.