Something a competent enemy easily could exploit with cloaking devices and superior sensor tech. Just stalk the lone patrols and when HQ gives the word, you ambush hundreds of unsuspecting Starfleet ships at once, probably crippling the Federation in the first two hours of the war. Why the Romulans never went this gamble seriously will remain a secret, forever. The thing is: you will not catch the Galaxies or Ambassadors off-guard. But the boatloads of Mirandas running supplies or staff? The Oberths mapping local space? The Excelsiors ferrying some Commodore/Admiral-desk job-brainlet? Yeah, I can see a peaceful Federation acting completley braindead. And I can see the Romulans or the Dominion burning the entire thing down, laying waste to hundreds of ships and then proceeding to sieging the shit out of underprotected core worlds.