they have a considerable amount of freedom and it's possible that their "Senate" represents a truly representative democracy. The fact that they are aggressive and xenophobic towards outsiders doesn't indicate anything about their internal politics.
That's what I was going for in my re-conceptualization of the Romulans: They're xenophobic and hostile to alien races but they treat their own people very well. They just have this "Manifest Destiny" thing.
The problem with that idea is that it's flatly contradicted by "Face of the Enemy" and, later, numerous DS9 episodes, which firmly establish that the Romulan people live of terror of the Tal Shiar -- they have plenty of horror stories about people being dragged out of their homes in the middle off the night and then being "disappeared" by the Tal Shiar.
The Romulan Star Empire may not be a totalitarian dictatorship a la Nazi Germany, but neither is it a state that indulges in liberal democracy and popular rights.