Based on this, the planet Vulcan, prior to Surak, expanded into neighboring systems with a warlike vigor.
Or then it did not. Quite possibly, the savage colonization period of Vulcan was over long before the local space age began - just like here on Earth (hopefully!).
Spock would simply be saying that people of Vulcan stock would be capable of atrocities like savage colonization periods - therefore people of Vulcan stock encountered in space can be expected to be fully capable of space savagery. Seeing pointy ears and green blushes doesn't mean the opponent would be calm and logical and pacifist; rather, barring the remote possibility that those folks had their own Surak, anybody with those racial traits should be considered a potential berserker.
As for the Confederacy of Vulcan thing, we could expect the name to reflect the makeup of the polity somehow. Is the Vulcan sphere of influence a politically organized whole? Or is it impossible to nail it down in terms any more formal than "Imperialist West" for the comparable sphere of US influence on Earth, due to the underhanded nature of Vulcan control over the players involved?
On the other hand, it is a Star Trek tradition not to pay much attention to the (current) factual meaning of such terminology, or indeed to defy all reason just for fun. What is "unified" about the Cardassian Union? Who are the "allies" in the Ferengi Alliance? We have yet to hear of an Empire that would actually have a sovereign of any sort in command - has the word lost all of its Earth-history meaning by the time of Star Trek? Is "empire" merely another expression for "ambitious"?
We never quite learn of any planet other than Vulcan itself that would be under factual Vulcan rule, now do we? There's the monastery on P'Jem, but even that could be some sort of a religious exception, a piece of Vulcan on uncontested Ufotarian soil.