Downtown Miami is home to several art attractions such as the Perez Art Museum Miami and the Adrienne Arsht Center for the Performing Arts. American Airlines Arena, home to the Miami Heat is along Miami waterfront. The Bayfront Shopping Center felt like a tourist trap and not much more of a waiting area for cruise goers to shop before take a boat ride around the Biscayne Bay.
If there is something special down here, I couldn't find it. Parking is expensive but there is a free monorail system with stops at all the major attractions. Slightly west of downtown is the Miami River and several waterfront dining options, including Garcia's Seafood Grille and Fish Market. Garcia's conch fritters had the perfect conch to flour ratio.