Blake,
The number of "success" stories in Negril is far, far less than 50%. After we discussed this matter with other ex-pats on the island, the number seems to be less than 5%. Out of each 100 people we know who have tried it, maybe 2 or 3 make it. This puts the situation in a proper prospective.
US citizens can only stay in Jamaica for 6 months in any calendar year. That is whether you have a business or not. If you have a business and want to be a working part of it, the government expects you to do the proper thing and obtain a work permit or become a citizen of Jamaica. If you are "investing heavily", a work permit would be no problem, either in cost or granting. The permit system is set up to minimize the number of people who think they can come to Jamaica and take a position in a job that a Jamaican would be able to fill.