The only reason a federation-romulan war has not happened until Nemesis is because the writers were not self-consistent:
A war was not depicted (only a very bitter cold war) - maybe they did not have the budget for a war, or the war would have been too serialized for TNG, or they had a lot of other plot lines on their hands, etc.
Why is that not self-consistent? Because the way the romulans were painted, war is inevitable.
Sure, go on denying anything that actually happened on-screen and pretending that the writers are stupid while you are the only guy who has figured out how truly evil the Romulans are and that total war is imminent.
There is a reason the Feds are engaged in a cold and not a hot war with the Romulans. First, as already mentioned this is a three player game, there are also Klingons. Second, Romulans prefer intelligence work, sneaking, spying, lying and so on. Their dream is to set up two of their enemies against each other such that they do not get dirty hands themselves.
Now if we talk about the Borg or the Dominion, powers that simply threaten to overrun you, this is an entirely different ball game and I am the first guy to point out that the Feds weren't prepared for these challenges.
But giving up a cloaking technology you wouldn't wanna use in the first place after some incident with the Romulans is hardly stupid. And let's please cut this Chamberlain nonsense. First, everybody was fine with Hitler in the thirties, not just one British prime minister. Fascism didn't hurt business. Second, last time people cried "no appeasement!" in the real world a country was raped by the West. I am not too eager to learn the false lessons from history to justify warmongering.
The idea that cloaking would confer a great strategic advantage seems quite off base. After all, Romulans can cloak at their leisure, yet they appear to be the definite strategic underdogs, always forced to attempt harebrained schemes to gain the upper hand (and always failing).
In general, giving up technology in an exchange where the opponent gives up aggression or territory is an incredibly advantageous bargain. Technology cannot be monitored, invisibility technology least of all, so you have given up nothing - whereas territory or state of war are obvious things the opponent can do absolutely nothing to obfuscate to his advantage. Basically, the UFP "gave up cloaking" and continued to cloak nevertheless, which must have been a great victory if the Romulans "gave up attacking" or "gave up the Outbackian Sector" and could do absolutely nothing to wiggle out of those quotation marks.
Indeed, it simply didn't matter much. Of course people can repeat ad infinitum that cloaking technology should give the Romulans a gigantic advantage ... but this is simply ignorant of what actually happened on the screen and hardly the basis for a Trek discussion.
It's kinda like saying that warp drive should not work and claiming that anything we see in Trek is thus impossible.