If you do a search of the FLA boards you will find several mixed reviews for Premier and other parking services in Miami. Some loved it and others hated it - there does not seem to be much in between ground?
Parking anywhere in downtown Miami or Miami Beach is expensive, with most hotels charging $25-30+/day for parking on top of the room rate.
Not sure about Premier, but there are parking operators who don't own a lot but instead lease a space to you in whatever close by lot offers them the best deal -- their profit is the difference between what you pay and what the lot charges them. Service in this situation varies from great to ugly.
Parking at POM costs $20/day and is convenient, covered and secure
. Parking anywhere else in Miami is not as convenient, may not be covered, and will not be as secure.
If you are looking for hotels offering cruise parking deals, try www.parksleepfly.com
but almost all will be out near MIA. If a shuttle is not part of the deal both ways (it usually isn't), plan on spending $50-60 for round trip cab fare to POM and then back to your car.