I think it's the eyes. There's less of en emphasis on using them in modern acting (especially TV), and celebrities -as opposed to traditional actors- are less likely to exercise that kind of discipline anyway.
Plus people in general probably assume Vulcans are wooden, just from pop culture. And that fans are socially-challenged people who go around mimicking Spock or something. So what's your typical TV actor supposed to do if he lands a ST gig?
'Unification' -- I would see as being product of a more episodic time when most of the planets visited by the Enterprise had only a dozen inhabitants on them, despite more progressive stories like The Undiscovered Country attempting to show otherwise. For every 'Sins of the Father' there was a 'Friday's Child' or a 'Private Little War' (really, why would a space-faring people like the Kilingons feel the need to negotiate or manipulate the natives of these dozen-populated worlds? They don't have a prime directive).
Anyway, if the Vulcan's really believe that "peace should not depend on force," maybe you really could occupy their planet with just a couple ships. It would be like occupying the capital and shutting down the government, however temporarily. The Federation could root them out, but time and policy would be a factor. There might even be pressure to dismiss a Vulcan/Romulan conflict as an "internal matter" much as what happened with the Kingon civil war in 'Redemption'. Does any of this excuse the writers... probably not. But the fact that Vulcans suddenly had a sizeable military (and were able to use it) on ENT probably should have been another clue that the three-parter would only end the way it did.