Well, the 2 party system in America is largely a result of not implementing the kind of electoral reforms many other countries have. In Australia, for example, they have the single transferable vote system, which basically allows people to vote third party but still have their vote cascade to a second choice so that no spoiler effect is present.
Parliamentary systems, overall, allow for more political diversity in parties and for the ability to form coalition governments. There are advantages to the American system, but political diversity isn't one of them.