We were there in March two years ago, and did not get a car. We just took a cab to/from the airport, and we found plenty of activities to keep us busy for the week. The public "tourist" bus loop was great, and made it easy to get anywhere we needed in SoBe, including grocery shopping.
You didn't mention what size of unit you have, but if it is a 1BR, I highly reccomend you request one of the units in the very back of the building. Those 1BRs have and extra window in the bedroom (out the back of the building), and it makes the whole place much brighter. The units are a bit small and can feel a bit cramped, but the extra window helps. Since I have been there, they have refurbished the units so they should be in pretty good shape.
Kurt