Sela plan was domed because it call for three real Vulcan cargo ships
But the thing is, it didn't.
The plan was to send Romulan "peace envoys" to Vulcan. Vulcans would know
they would be Romulans coming from Romulus. So there'd be no point in not
sending them in Romulan ships.
Indeed, using old Vulcan ships would just confuse the issue and make everybody suspicious: why are these Romulan peace envoys using old Vulcan ships? Where did they get them? If they are space pirates who steal Vulcan ships, how can they be taken seriously as peace envoys?