Precursors: Played straight – but not completely. The species generally referred to as the Precursors got the name for having some of the most extensive local influence, and for being the species that made the eldrae, but in practice, they’re most notable for (a) being one of the oldest (but not the oldest) of the elder races, and (b) being not around any more, almost certainly through self-induced war-extinction. Certainly not the first race to ever gain sophoncy in the galaxy; there’s plenty of evidence around of older species yet.
(Also, reputedly, near-solipsists who were literally incapable of conceiving that another entity’s opinion might actually matter, short of a major mental break. This might just have something to do with why they aren’t around any more.)
“The Starfall Arc is old, its history a tale of fourteen billion years. A tale, moreover, littered with elder races, ancient Powers, and primordial civilizations godlike in their power – very few of which, and none of the oldest of which, remain extant in the present day. We know the galaxy to be rich in life, to go on generating new life, and to have been so for many eons before the modern era. And yet the civilizations of the ancient past that could have colonized the entire Arc a million times over have all fallen and disappeared long before reaching such an apex.”
“What may we learn from this seeming paradox?”
“Clearly, that the power of the gods is not enough.”
– Darkness and Silence: The Empty Past,
Higher Tech Species: Lots of them, arguably. The Imperial member species are this for most, if not all, of the Associated Worlds. The elder races – which, despite the technical definition based on the information entropy of their communications, in practice means “significantly older than the oldest of the current galactic mainstream” – are this to everybody, although nearly all of them aren’t particularly active any more, and have, for example, retreated into a virtual civilization in their own “Happy Fun Ball” (for which read, the matrioshka brain about eighty light-years to nadir of the Cordai Gap). And finally, of course, the Precursors, who would be this to everyone except that they’re simply Sufficiently Advanced Aliens.
Ghost Planet: Quite a few of them, in various locations – the Galaxy is veritably knee-deep in elder-race litter; as mentioned elsewhere, this gives the existential-threat people something to worry about, and also enables companies like Probable Technologies, ICC to make an entire industry out of archaeology.
(Since I oopsed and didn’t post one yesterday, this is the first of two tropes-a-today.)
Older is Better/Lost Technology: Subverted in that while there are some awfully nice bits of leftover Precursor and/or elder race technology around, and piles of interesting things buried in the archives (assuming that some leftover perversion doesn’t eat your soul when you go looking for it), it’s more or less absolutely averted within the lifespan of any given civilization. Things get better, not worse, the more so for those people who are appropriately obsessive about not losing stuff along the way.
And in any case, in many areas, modern civilization has beaten the best (extinct) elder-race tech that’s been found. After all, it became the starting point for development.
“Five scientist-explorers were exploring an abandoned outpost in the Expansion Regions one day when they came across a freshly-excavated artifact, still humming with power and covered in unknown controls.
“The first, a galari, said ‘We should transport this back to our laboratory, so that we can investigate it properly, and spread the word of our discoveries. Think of what we could learn from it!’
“The second, a kalatri, said ‘Take it to our laboratory, yes, but we must keep this quiet. It could be dangerous, or disruptive, or corrupting. It is best that people do not know of it until we can be sure they will not be harmed, and use it well.’
“The third, a codramaju, said ‘We should keep it quiet, but so that we can master it before others know of it. We could build a hundred new technologies with what we learn, and be wealthy beyond our dreams.’
“The fourth, a linobir, said ‘We should master it for its power. The elder races built machines powerful beyond imagining. If this is one of these, the galaxy would be ours for the taking.’
“But the fifth, an eldrae, said nothing – for with the press of a keyswitch, both he and the artifact had vanished away.”
– anonymously-posted extranet joke