That said, they are the North Koreans, no matter how they dress. They come in a package where Vulcan is South Korea, and animosity across a Neutral Zone revolves around blood ties. Their policies are those of North Korea, with insane aggression for aggression's sake to keep th mighty (perceived) enemies on their toes, but with no desire for actual confrontations where the apparently puny realm would be annihilated. They are the party without allies, save occasionally for the #1 adversary of the UFP, whoever that happens to be at the time; Vulcan's South Korea is solidly supported by an alliance.
Inside, Romulans may cosplay Old Rome, of course. But Old Rome also had its North Korean traits: blind aggression for aggression's sake was a shrewd maneuver in inner politics, the assorted private little wars helping lowly Praetors grab personal riches while the Republic at large was indifferent to the meaningless fights.
Yet Rome did rule, and expand, and lead. Romulus never did, and probably never will. So looking from the outside, it would be inconvenient to think of Romulus as the Space Rome...
...Unless, perhaps, they once were. Like, say, 2,000 years ago. Now how cool would that be? Alas, we hear nothing of this glorious past in any context, including time travel adventures. Oh, well. At least we get nice old Romulan ruins across the galaxy.
Timo Saloniemi