Something has to be tried in order to at least normalize relations between North Korea and South Korea, and at best reunite the Koreas. North Korea is clearly never going to be the first or most aggressive party to look for peace or understanding, so its up to the South to extend a hand to them.
While the Sunshine Policy ended in 2010, I do believe that it would encourage further development of nuclear weapons and materials in North Korea. In 2006, when nuclear and missile tests were undertaken by North Korea, South Korea punished them and their relationship began to degrade. Even in 2010, North Korea was testing missiles. It is easier to develop the weapons with the Sunshine Policy.