Let's check the fictional history of Trek.
2311 - Treaty of Algeron
2379 - Contrary to the warmongering notion that Romulans are devils who would never ever want peace (why then did they sign treaties with the Feds in the first place?) the events of NEM imply the chance for a real peace. Of course we are not naive, we all know that unlimited expansion is THE Romulan dogma. But even the most rigid Vulcanoid societies can change.
So yeah, looks like the few decades prediction has not come true which is hardly surprising.
If you view the Feds, the Klingons and the Romulans as the three main powers in the region we have a three player game. And such a game does not imply all out war (if A attacks B with all he has like in a 2p game C will stab him in the back) but rather the striving for a balance of powers. If someone is weak somewhere the enemy will tickle him a bit but that's it. The one wildcard in this game are the Klingons, they do not necessarily mind to take some chances and perish in glory. But the Romulans are fairly predictable, they will only strike if they can afford to attack the Feds without weakening their defenses against the Klingons.
Add the alliance between the Feds and the Klingons and it becomes obvious that the Romulans will not seek war as long as a rough balance of powers is maintained. The last war happened in the 22nd century and it was most likely devastating for both sides. Afterwards there have been some border incidents and the usual Romulan sneak tactics of spying and subverting. If you wanna keep the Rommies at bay you better make sure that you have decent intelligence services.