I think it's important to note that the last multi-polar "era" ended with the World Wars. The ascedence of German power unbalanced the system established at the conclusion of the Napeolonic Wars (though it. There are also some assumptions inherent in any kind of measurement of polarity -- first, that states are security-focused; second, states are the dominant powers in politics; and third, that the organization of the international political system has a direct and major impact on state policy and decision making. All of those assumptions can be challenged. Realism is a sound theory if kept within its left and right limits. But as Stevely noted, those limits can be severely restrictive.

I'm more inclined to accept the omni-balancing theory that domestic factions leverage all aspects international relations for domestic gain. So to answer the question, IMO the utility of a multipolar world for the US will depend upon how effective the US can and is willing to take advantage of it. And that in turn will depend upon the characteristics of the political arena here at home.