No you are not mistaken. The (former) Marine Hotel which your ancestor moved to in 1853,is still there,but as a private residence.As you may know,it was opened in 1954 by Princess Margaret as "The Sunshine Home for Blind Babies but closed in the late 1970's.
Close by in Southerndown village is the former Dunraven Hotel which opened in 1890 but in 1948 became "Southerndown Home for The Blind & Elderly."It closed in 2009 and is still for sale.
In response to a 2011 inquiry from a Terry Morgan about the Marine Hotel, you mentioned his ancestor who moved into the hotel in 1853. That “ancestor” was either proprietor Samuel Howells—who was my great-great-grandfather—or one of his children). I have a lot of information about Samuel, the design and building of the Marine Hotel, his ancestors, and his descendants (one of which owned Pen-y-lan Farm in St Brides Major before emigrating to America). I would like to discuss with Terry Morgan and/or you if there is interest. Phil Howell, Marietta GA, USA.