It really depends what interests you have.
We were in the Miami area late last year and had a great time.
What I enjoyed in the area was:
The Wolfsonian Institute http://www.wolfsonian.org/visit
The buildings in the art deco art of Miami beach.
Vizcaya Museum: http://www.vizcayamuseum.com/plan-general.asp
We stayed at Biltmore Hotel which was an attraction itself.
This is just a couple of suggestions there are plenty of interesting things to see and do.
The guided tours of miami, coconut grove, etc are great.
*) Eat the cuban food and have a "Cafe colada" Rich black coffee with lots of sugar
*) See the venetian pool coconut grove near the Biltmore hotel.
*) Eat at Culebrinos Near 25th street and Brickell.
*) Drive across the venetian causeway. From Brickell Ave next to Marriott Biscayne Bay to South Beach
*) See Lumus park on south beach.
*) Come back across the MacAuthur causeway, turn into Star island. There is a guard shack but just tell them you are looking around. It is not private. They will just say stay out of private residences.
*) History of Miami Museum downtown same complex as Miami LIbrary.
*) Eat dinner after dark at Rusty Pelican, Rusty Pelican Miami Just across Rickenbacker causeway. Upscale but not rediculous. Best view of Miami at night from across bay. Or Garcia's on the Miami river near 10th ave. Garcias Seafood Grill and Fish Market | Miami, FL | 305.375.0765 Best stone crabs, FL lobsters, seafood reasonable prices.
That's about all you have time for.
I like to stay at the Miami Biscayne Bay mentioned above. Skyline is awesome at night.
sounds like the tour I took on my cruise stop.
I had been to Miami so many times, just passiing through, and never really had the time to see Miami, that I actually took a cruise out of the Northeast that had Miami as a cruise stop (as well as Key West being a person who does not like long car trips).
I have to say the tour was great, we pretty much hit everything on your list above with the exception of eating on shore.
There are some great suggestions listed above. Will you only be staying in Miami one night? It's not too bad of a drive from Orlando to Miami on the Turnpike. If you're driving at dusk, sometimes you can see some of the small Florida deer near the roadside.
A cruise down Calle Ocho is a must, stop by the Versailles for lunch or at least a pastry with cafe cubano Versailles Restaurant - Miami - The World's Most Famous Cuban Restaurant
Personally, my favorite dinner spot in Miami is Michael's Genuine Michaels Genuine - Fresh, Simple, Pure. The food and energetic Miami vibe make it a fun place. It's located in the Design district, which is not as crazy as South Beach or downtown.
Another thing that's always nice to do is the cruise around the houses, etc. that departs from Bayfront. It's not too long, but is a pleasant way to experience Miami from the Intercoastal Waterway. A nice thing to do at sunset or nighttime.
The next morning go hang-out and people watch at South Beach. If your here past October 11, it's stone crab season, so you can have lunch at Joe's Stone Crab http://www.joesstonecrab.com/
I haven't flown on Spirit either but according to their website you can bring one personal item like a small backpack, briefcase, or laptop on for free as long as it fits under the seat in front on you. They do charge for the larger carry on bags in addition to checked luggage. Here is a link to their baggage fees:
Even with one checked bag paid online for $28 in addition to $39 for the one way ticket from Orlando to Fort Lauderdale it is still a very good deal at $67 and beats driving 3.5 to 4 hours to get there.