The Romulans have been called "Space Romans" in the past, but how accurate is that? Roman Society lasted for a thousand years and went through many changes, Rome started as a republic and became a dictatorship, had something akin to Monarchy for a while, until the end of the Julio-Claudian dynasty. That's not mentioning the Holy Roman Empire and the period where the Roman Empire was split into two different empires, an Western and Eastern one.
So what era of Roman Society are the Romulans based on? Is it a democracy or a dictatorship? Who holds the real power, the Senate or the Praetor? Is the Senate elected or appointed? How are Praetors selected?
Also the Roman Empire was never really xenophobic, it made the people they conquered Roman citizens and even tried to improve their lives in some ways, usually by improving road systems and building aqueducts. The Romulan Empire doesn't seem similar to the Romans in that important respect.