There are plenty of taxis at Miami International. I would not recommend the Super Shuttle as they have to fill the van with passengers first. They tend to stop at several terminals before you ever get underway. They only charge about $10 or $11 each, but if you have two or more in your party, you could have gotten a taxi (yellow cab type) for about $20 plus tips.
The taxi is faster. We got to the pier in about 15 or 20 minutes, this included the stop to show Custom booth official our I.D. (Sunday afternoon about 1:00pm). I think the distance is only 8 - 10 miles.
This was in July of 2002, so I don't have current rates or know of any procedural delays that may have occurred since then.
I forgot the last part of your question. You can easily get a taxi on disembarkation. You can also purchase a transfer (bus) on your cruise at the pursers desk - about $10 each, as I recall. We sailed the Norway on our first cruise in July 2001. This is a "Grand Lady" in the true ocean-liner design. This is an excellent choice for a first cruise. You may want to try one of Carnivals or Royal Caribbean's big ships after this, just to see what the new ships have to offer. Happy cruisin!
Just make sure you dont get a cabby that will screw you, I live in Miami and took a cab from the airport and the guy wanted to charge me 40.00 for a trip that was suppose to cost may 10 at most. I told him off on the way back to my house because i told him that he was taking me the long way, after much arguing he admitted he took the long way to get to my house for more of a tip.
From MIA to the Pier its probably a good 30.00 dollars, there are PLENTY of cabs, everywhere!!!