I agree with all of the above. Particularly Kevin. In January, we were scheduled to get in earlier (~1:30, I think). But we were then delayed a couple of hours getting out of MIA. Then we had to wait a looong time for bags to come out. So we would have been hosed a bit if the same events would have transpired with a scheduled 3:30 arrival. So I may recommend having a plan E in the back pocket, and that's a private water taxi. Per Kevin's recommendation, I also had this contact info ready to go (no guaranty that the rates are current or that he would be available at the last minute). Others will give similar recommendations, I'm sure. I would only recommend keeping it handy in case you have connection/arrival problems and need to start working on other options from the airport bar.

Raymond; VI Water Taxi
(340) 690-1251
$350 to west end. (9pm close)
$425 to RT (7pm close)