Did you consider renting a car for the two days - bringing it back to Ft. Lauderdale and taking a shuttle back to Miami? The reason I ask is because I just called Thrifty Wednesday morning a rented a car for next Friday. They wanted $77 per day and I asked if there was any special deals. After a couple of minutes on hold the person came back and I could get a premium car for $46 (tax included). We're going on a cruise the next day and they have free shuttle service to the port. They also have free shuttle service to the airport where it's easy to get shuttle service to the Port of Miami. It's only a 45 minute drive from Ft. Lauderdale to Miami. If you could get a premium car for that price it might be worth it. There's room for 5 pcs of luggage in the bigger cars. The agent didn't know about any special deals so you have to ask.
Another thing about getting a car is that you can get a hotel anywhere and still go to the Bayside Market Place.