The situation in South America is not relevant, there the issue is political as many countries view America as "an enemy" or unfriendly nation. Spain, being part of Europe views the US as an allie, so holding US citizenship should not be an obstacle.
That said, the Spanish banking system is in chaos at the moment, with many banks being forced to merge and government bailouts being given to keep them solvent. So I would seriously think twice about banking here.
Before you can open a bank account in Spain, you will need to apply for a NIE number, this is an identification number for foreign nationals that permits them to hold money and property in Spain. NO transaction is possible without one. They are usually applied for via the local police office in the town you intend to live, you can find more information on the website of the American embassy (which I believe is located in Madrid).
Migration from America to Spain may require a visa, (I moved here from the UK so the rules were different) again the US Embassy is the best place to start.