On a per-mile basis, these First Class fares are hard to beat

Dividing the price by the miles flown is a way of leveling the playing field when comparing airfares to different destinations. With the difference, you might even be able to upgrade your hotel room to an ocean-view suite. It also tells you how far a buck takes you from your departure city. Caribbean First Class fares, often $600 to $900, stack up well in comparison to lower 48 states First Class ($900-$1,400).
We surveyed over a dozen routes and found that the following destinations have First Class fares $600 to $800 from many US cities: Montego Bay, Santo Domingo, Turks and Caicos, and Bahamas (Nassau). Many other destinations are available for another $100 to $200.

Low First Class fares to the Caribbean began in 2002 when US Airways, trying to avoid bankruptcy, slashed fares to less than $1,000, a level rarely seen ($1,600-$2,600 had been the norm). At the same time, the carrier launched a slew of new routes to the region, and the two initiatives drove down fares overall as other carriers matched US Airways.

No need to use miles to the Caribbean…

With fares this low, it doesn’t make sense.

…Or 2-for-1s…

Buying two published fares will usually cost you less than using Continental’s (Amex IAP) or United’s (Ameniti.com) 2-for-1 programs because they’re valid only with full fares. These usually cost more than twice the lowest discounted First Class fares.

…Or elite upgrades

In this case, they’re a lose-lose proposition. If you’re flying American or United, the surcharge could bring your outlay close to that of a paid First Class fare (and you can’t confirm until just before departure). If you’re flying Continental, Delta, Northwest, or US Airways, which all offer “free” upgrades to elites on Caribbean routes, you’ll have a lot of competition, especially in peak season.

So, why play elite upgrade roulette when there’s a sure bet?