Democracy in Central America has had various impacts, but among the options you've provided, the most relevant would be increased control by the United States.
Historically, the United States has played a significant role in Central America, particularly during the Cold War, where it sought to counter Soviet influence in the region. This often involved supporting or undermining various governments, influencing political systems, and intervening in the region’s politics. While democracy may have been promoted as a means of stabilizing governments, it has often resulted in increased U.S. economic and political influence, with the U.S. exerting control through various means, including military aid, economic support, and trade agreements.
The other options you mentioned—dependence on Spain, increased economic prosperity and stability, and increased restrictions on trade—do not accurately reflect the predominant trends associated with the impact of democracy in Central America. Instead, the democratic processes have varied widely across different countries and contexts, leading to mixed results regarding stability and prosperity.