Turnpike is your best bet. I95 is always under construction, and is a nightmare in Miami through WPB, and after that it veers east, away from Orlando. At night it's usually a smooth trip once out of Miami/Broward. The rest stops are also safer as they are well illuminated and continually patrolled by police and have gas stations in case you need to refuel. I95 rest stops are pretty dark, and don't offer much in security or needs. Vending machines and restrooms, if you need gas or real food you'll have to get off the highway and pray. You can save a little money on tolls by buying a Mini SunPass for $5.00, that money goes towards your tolls. If you are driving back to Miami afterwards, without SunPass tolls will be close to $50.00 (+/- $25.00 one way), with it, you'll get a bit of a discount and you'll zip through the toll plaza's. If you do decide to buy the sunpass, buy it at least one day before your trip as it takes a while to activate, and you'll need access to the web to register (iPhone or similar will work) and verify that it is active before using as the fine for zipping through the SP booth is hefty.
You will get a lot of traffic leaving the race, and it will be pretty thick for most of Miami. Bring your patience, and if you are not familiar with Miami, use highways whenever possible, the thugs can spot a tourist a mile away. If drinking at the race, desgnate a driver, not only for your safety and mine, but there are often a number of sobriety check points littered throughout Miami. Also, check to make sure that there isn't a game or concert at Landshark Stadium, if there is, stay to the left lane of the Pike when you approach the Dade/Broward line and you should be ok.
In Miami, bring your appetite and be sure to sample some of the wonderful Cuban restaraunts throughout the City, and if possible try to enjoy the night life.
Other than that, wave to us as you pass through WPB, we'll be heading up that way in December.
Hope this helps.