Aren't the Romulans the Russians? The Klingons always seem to just be doing random war things and were mostly just doing their own stuff, whereas the Romulans seem to have some kind of actually coherent strategy.

I never got "communist" from Star Trek. There seemed to be very limited top-down control outside the military, trade seemed to be an important backdrop, and automation largely replaced the necessity for people to fill any particular role. So what it seems like is a low-touch society where automation serves the needs of the common people, but operates within a capitalist framework. If it was communist, I think we'd see a lot more conflict between the various races, but they're largely happy with the equilibrium they've struck (outside various periods of conflict).

I think if we were to explore the Star Trek universe, we'd see a lot of corporations and whatnot controlling significant portions of the interstellar economy. But since we largely follow military and diplomatic groups, we just don't see what the rest of society looks like.