One would assume the writers had the Korean reunification foremost in mind when writing "Unification". After all, 'em pointy ears have always been something of an Asiatic analogy, despite being superficially ancient Roman - mysterious, disciplined, with strange arts and passions and a chillingly fascinating custom of suicide when cornered, as opposed to the simple Russkie-analogy brutes of the Klingons. And the terminology and methodology of the Vulcan-Romulan separation, including the Neutral Zone, extreme isolationism, and insincere gestures of goodwill, is similar to that of the Korean split.
The analogy has never been exact, of course. Korea was divided in the aftermath of a war with an external enemy, and was kept divided because it served the interests of greater powers using the halves as pawns. And North Korea, while no doubt intent on aggressive reunification on its own terms, has never been a superpower in the sense later Trek seems to suggest the Romulan Star Empire is.
Then again, Romulans were depicted more as bit players (albeit very aggressive ones) in TOS, forgotten for a century and then only noticed because they were absurdly territorial about their prison-like nation. It could well be that this is their true role in the TNG era as well, and that their military significance is similar to that of North Korea: a source of superpower-level technology on weapons of mass destruction (in this case very impressive starships) disproportionate to the size of the nation.
Also, cultural and political issues separating the two halves of Vulcanoids might be skin deep, and commonalities might be legion, as with the Koreas. If a reunification were achieved, it's far from said that the Vulcans would stay loyal to the Federation, as membership in that organization could have been but a vehicle for them to deal with the Romulan problem.
Timo Saloniemi