The attempt of uniformization and subjugation of the regions conquered by the empire (Syria, Germania, etc) really reminds me of the modern colonialism. The distinction of "barbarian" and the sentiment that the Romans are the "more civilized", the "more sophisticated", the "benevolent power" that bring light to the savages, too, reminds me of colonialism.
This is a wild, uneducated guess of course. But is it possible to see Roman Empire as a colonialism rather than a civilization?
This civilization-colonialism dichotomy relies on some codified definition of civilization, which is hard to come by. If I major in Classical Civilization, "civ" really refers to the Greco-Roman, Mediterranean complex of culture, art, government, language, and the like that really doesn't fit well under any other title. One can certainly call groups subjugated by Romans "civilizations." The idea of civilized you appear to be discussing is that put forth by 19th-c evolutionary thinkers who did set a list acheivements necessary to be a "civilization," but this view is considered antiquated, simplistic, and Westernized. But by either definition, I fail to see why a "colonizing civilization" cannot exist, that Rome must be either or. In fact, it would seem rather difficult for any colonization to occur if you did not have a distinct culture/polity.