Octavian states that there was a deliberate plan for an extended policy of imperialism. "Imperialism," as defined as concerted national policy of conquest of outside cultures for the purpose of extending political and economic control in efforts to dominate the resource base of a given territory, would indicate an offensive action taken on the part of the Roman Consuls.
This is not the case. The majority of battle that take place after the annihilation of Carthage in 146 BCE are defensive in nature. Even the attack on Carthage was in response to the battles for Sicily, Corsica and Sardinia in 241 BCE and Hannibal's expedition through Spain ending with his defeat in 201 BCE.
Beyond that the attacks by the Allobroges and Arverni, the Cimbri, Teutones and Ambrones, the Volcae Tectosages even into Caesar against the Sueves, the attacks were offensive strikes in a defensive campaign.
"Imperialism" was simply a byproduct of the Roman Empire's positioning. Their territory was directly impeding the migratory paths of the outlying tribes. This is the reason for Rome's perpetual need for defense.