SAN FRANCISCO - High in a downtown hotel, Nicaraguan folk dancers twirl in lacy white dresses, their bare feet tapping intricate rhythms on the wooden stage, giving their buttoned-down audience a bit of tropical warmth on a foggy afternoon. Their flounce and easy smiles before this roomful of travel experts are part of an effort to promote Nicaragua to Americans who might choose to retire there, attracted by its pristine beaches and colorful culture. And then there are the tax breaks and other incentives that baby boomers are likely to find even sweeter than the tropical fruits the dancers carefully balance in baskets on their heads. "They're a growing market with disposable income looking for a place to live, and Nicaragua has that," says the country's young minister of tourism, Maria Rivas.