The idolization of Rommel or Napoleon had no relevance on keeping Germany or France strong
Indeed, in both cases it took place after
strength had been denied the respective foes. But like you yourself emphasize, it's not the defeated that gets to decide whether to rebound or not, it's the victor and all those little quirks of his that have little or nothing directly to do with the struggle at hand. Klingon mindset does seem to call for playing up the strength of the foe, as the heart of fighting lies in the ability to tell stories about it. At the time of TNG, actual physical spoils of war seem to play little role for the Empire: it's not as if they would really need a Cardassian mining world or prize fleet for anything much.
Indeed, in "Way of the Warrior", it seems Gowron goes to war with the principal goals of a) looking good and b) getting as many Klingons as possible killed - at least from the ranks of his domestic opponents. That he later digs in does not appear to reflect any physical demands of the empire: what Klingons do with their newly annexed territory seems to be random terrorizing of Cardassia, as in "Return to Grace" and "Rules of Engagement", rather than exploiting of resources already gained.
The romulans wanting to resurrect an enemy - their enemy - just so they can annoy the klingons, would come at the same price of making the romulans idiotic cardboard characters.
How so? That's straight from the real world: whenever the big wars in Europe seemed to be leading to a decisive victory, somebody on the winning
side would decide to disrupt the process in order to restore the balance and deny his allies the potential boost to their hegemony intentions.
Remember that while Klingons had border quarrels with Cardassia (at Betreka), Romulans supposedly had none. Annexation of Cardassian worlds would in all likelihood give the Romulans isolated bubbles of territory outside the main body of the Star Empire - a terrifying prospect for a people who have been huddling inside a Neutral Zone for more than a generation (which for Vulcanoids is pretty damn long!).
Potential for conflict abounds.
Certainly so. And since the actual sides in the conflict would be the strong victors, the rise of Cardassia would be largely irrelevant in the threat sense - it would be merely a means for the true players in achieving their goals in this conflict.