Cuba would benefit, but would Castro? Is it a coincidence that the longest serving leader in the Hemisphere (world?) is the one with the most economically isolated subjects?
No, I don't believe it is a coincidence that isolationism has aided Castro in oppressing his people. Just as the emergence of capitalism in China has kept the Chicoms scrambing to squash dissent, trade with Cuba would allow the Cuban people a better standard of living which wouldn't necessarily be a good thing for Castro.