Melbourne central is just a shopping centre adjacent to Central Station. It's no more or less interesting than any other shopping centre really.
Bourke St Mall is NOT part of Melbourne Central ( don't know who linked the two together on this site). It's famous for the two major stores, Myer and David Jones, and in particular, for the Christmas window display at Myers. Lots of buskers in Bourke St Mall, and access to several of Melbourne's arcade, such as the lovely old Royal Arcade, with it's famous clock with Gog and Magog who strike on the hour. IF you go in Royal Arcade, treat yourself to coffee or chocolate at the chocolate shop.