I don't admire the Romans (this isn't some sort of RETVRN posting), but I think you have to recognize they played a certain historical role in Europe, Africa, and the Middle East. Much of western European culture rests on a Roman substratum. They advanced the productive forces in the empire, and when that historical role was completed, they were conquered by "barbarian" tribes who had developed a higher level of production -- namely, feudalism. Michael Parenti has written on this.

You're absolutely right that Americans do spread culture, and way too much of it, but -- it's a weird sort of cultural export, corresponding to the basically negative essence of capitalism in the historical-dialectical process. For the most part, it's either 1) the basic technology and social structures of modernity, which by historical accident they possessed in the most developed form, or 2) a cultural art-product that is completely corrosive and negative, a sort of "anti-culture," if you will. This latter is the superstructure, not of a social order, but of an anti-social one. Now as regards 1): nothing about it is uniquely "American," and in fact the American version is flawed at its base, due to it being organized according to the profit motive. In the People's Republic of China, productive mechanisms developed in the US are being transformed and superseded, a process of de-Americanization and corresponding Sinicization. For 2): American media/music/etc., being global but only in a capitalist sense, is essentially devoid of content. It is pure formalism, whose only value as a cultural art-product lies in certain purely technical advances: particularly in the art of cinema. As capitalism gives way to socialism, and countries break free of the imperialist yoke, these technical advances will be adopted and used in an art which is no longer "global" and "American," but is rather expressive of the values and desires of the proletariat of a particular socialist society. Particularly as the primary stage of socialism gives way to the stage after it, we will likely see a flowering of proletarian art comparable to any of the great artistic periods of the past.