The Star Charts eggshell was indeed designed as a compromise between the "Balance of Terror" statement of complete Romulan encirclement and isolation, and the TNG reality of Romulan free movement. I assumed the RNZ was originally agreed to be solid, but the Feds only existed to one side of the eggshell (actually, three sides, since the known location of the real Gamma Hydra combined with some assumptions to necessitate this) and couldn't readily control the other side. So in practice the RNZ began to "leak" as soon as the Romulans regained their strength and started to expand again, and the UFP accepted this de facto state of affairs de jure at some point...
As for the "Unification" plot, I'd also rather keep it apart from all other arguments because it's a world of pain unto itself. But I like to think that it does make sense - only our heroes were too stupid to realize this.
I mean, what did the Romulans say they were doing? They said they were sending an invasion army to Vulcan. Isn't the logical conclusion then that this is exactly what they weren't doing? They are the villains; they tell the captured heroes X; they then let the heroes escape from the friggin' homeworld of villainy unscatched. Doesn't that more or less confirm that X=untrue?
There would be many reasons to send a peace envoy to Vulcan in old Vulcan ships, then destroy those ships.
1) Get rid of the peace envoy, in a politically expedient way. Romulans don't like peaceniks, yet they do have an infestation of those, thanks to Spock. So why not enlist Spock's help in massacring the peaceniks? And why not invite Starfleet to witness the massacre, and cheer?
2) Confuse the enemy. That's always a good thing. And noisy old Vulcan tubs are great at masking the presence of a large and advanced Romulan battlefleet under cloak.
3) Impress your cronies. By "aborting" an utterly audacious "invasion" of Vulcan, Romulans gain massively in prestige points among all UFP enemies - a welcome improvement in their image after all the recent times they had to withdraw after Picard exposed their plots.
Note that the RNZ never really featured in the plot of "Unification". Surely any ship coming through the Zone would be challenged, be it Romulan or seemingly Vulcan? But these ships weren't challenged, which suggests that they didn't come through the Zone; that the Zone allows many sorts of traffic, just not Romulan or Federation warships; or that the RNZ actually borders on Vulcan.
That latter option is actually pretty interesting. In STXI, a spatial anomaly at the Neutral Zone was associated with seismic activity on Vulcan, as per Chekov's shipwide announcement. It doesn't make any sense for Starfleet to make that association, unless the NZ (the RNZ?) and Vulcan are spatially close. And Romulans are estranged Vulcans - perhaps a chip that has not fallen all that far from the old block in spatial terms?
I doubt Romulan space would border on the Vulcan star system as such; many episodes contradict this. But it's perfectly possible that "Vulcan space" is a subdivision of the UFP, and encompasses old Vulcan territory from the time of ENT, mainly in the direction of Romulus. Quite possibly the UFP border that brushes against Romulan border where the Vulcan tubs crossed is in fact Vulcan border...
The Star Charts weren't drawn with this in mind, but they can sort of accommodate the idea. The ENT material in there was a bit ill conceived anyway, based on just the first season of the show. It wouldn't be difficult to interpret ENT so that Vulcan-associated locations indeed extend "northeast" from the homeworld of the logicians, to meet Romulan space.
Timo Saloniemi
