Here's my shot at new Fallen Empire ideas:
Fanatic Individualists - Hedonistic Debaucherers. Their citizens are too busy engaging in pleasant activities to be productive, so they don't construct buildings, do research or colonize planets if you retake them. The only reason they maintain a military is because the assemblies for the ships are automated, and because some of their people find military life enjoyable, either because of bloodlust or because the uniforms attract ladies/sirs.
They are highly arbitrary in nature and act as fancy strikes them, but they do recognize the will of others, so they might or might not attack you if you are too warlike, as that must mean that you like fighting as well, or if your average happiness is too low and they can't stand it, or really if they feel like it. On the plus side, you can usualy placate them with gifts.
Fanatic Collectivists - Communistic Planners (could use a better name). Consumed by a communistic revolution at some time in their development, they are stagnant because a planned economy doesn't really work that well. They live behind the iron curtain, their leaders hiding from them the fact that your living standards are much higher than theirs as all money goes into building up the fleet. To keep the populace cowed, they will occasionally target the weakest empire they can find to fight a quick victorious war. If you're targeted, you may speed up the process by sending a proclamation of surrender, losing influence in the process.