This was never actually used for a game (or at least, I haven't used it yet), but I thought I'd toss it out there to see if maybe one of you might draw some sort of inspiration from it.
Essentially, near the galactic core, there was a very advanced alien culture that once existed - how long ago they went extinct is really pretty irrelevant. The truth is that their culture really was advanced - enviably so. Their art was gorgeous, their music stirring, their philosophy stunning in its insights, etc. Essentially, a culture so grand and rich pretty much everyone who encountered it would want to copy it.
That was also their major problem - they were very proud of their culture and couldn't really imagine anyone not wanting to be them. Of course, they were also very morphocentric - they believed that while they were not perfect (far from) they were the best suited to appreciate their glorious and beautiful culture.
Also, like most other races pointed out in Traveller, they didn't develop a stardrive. Accordingly when some suns near their own triple-sunned homeworld began to show signs of going nova, they knew they were doomed as well. However, if their own extinction wasn't bad enough, the scouring of their homeworld by the cataclysm that would follow was intolerable to them. Being beings of resolve, they decided to do something about this.
For the remaining years before the waves of radiation and similar nasty stuff from the nova explosions reached them, they bent their entire efforts into making some way to cheat death, and they eventually did - they developed a way that future travelers could find their world, the special vaults contained within (a la Clarke's "The Star") where their cultural treasures were kept. However, also kept within were sophisticated psionic-technolocial computers which neared AI in their brilliance. These computers would only activate upon visitors breaching the vaults, and would strive to quickly learn to communicate with their new visitors then ... turn them into the long lost culture. They would become posessed or dominated by the desires of the computers, and using the amazing knowledge, would work feverishly to replace their own biology and culture with that of the long-lost ones.
That's what happened to the Zhodani - the explorers of the vaults learned to communicate with the amazing computers, then began working on retrovirii and so on - the female Zhodani explorers began bearing young of the culture (and not human babies), the explorers quickly became culture-human hybrids for the remainder of their lives, living them out to educate the newly reborn culture.
This was my idea for the Princess Wave destruction of the Zhodani - they were being culturally and biologically replaced by an alien race, with some Zhodani accepting that the aliens were superior to humans (such is the seductive quality of the alien's culture) while others horrifically only felt doom as they felt their biologies and children being subverted - and the spread of the newly ressurrected alien race and their human-alien hybrids. Being psionic, it was the Intendant and Noble classes subverted / assimilated first, with the Proles helplessly watching - this sense of doom being what the rest of the Zhodani are feeling, which is what is causing so much strife in Zhodani society as of around 1130.
What Strephon saw - the Queen and all that was the initial Alien culture's projections - that everything would be better, that everyone would be united in beauty and enlightenment. The longbow stations destroyed were destroyed by the Imperial Marine security detachments when they discovered the overcome Imperial psions trying build jump drives to reach the places where the alien computers were cached...
