They don't imprison Americans... tourism is their main source of foreign spending. And especially now with Raul in power, he may not be doing anything to help lift the embargo but that's only because Fidel is still alive and supposedly in better health. They only imprison domestic dissidents and political activists.
I've been to Venezuela, and you'd be surprised. Most of the people are happy. Now, that's to say the majority of the people were living in horrific conditions pre-Chavez. Now at least even the poorest of people in Caracas have cable tv, healthcare, and running water. So although the rich don't end up benefitting at all from gov't programs, the majority of people enjoy a higher standard of living.
People always think South America is backwards, when in reality they're just backlashing against the unjustified U.S. interventions there. Chile had a democratically elected Communist regime that was overthrown by a CIA-backed military coup led by Augusto Pinochet. Then came 17 years of political imprisonment and assassinations. Democracy doesn't always work, much less when the U.S. forces it.