Space Jockey near extinction

I figure something along the lines of this is possible, not so much "dying race" but thats generally how they work, perhaps they seed a planet - which takes 'a very long time' to become truly hospitable then they colonize it: perhaps they engineer something like Humans as an intermediate form, readying the planet for their own use of it. this is where the horror would come from, we discover that we were engineered for a purpose but it will be more like organs spare parts etc ( as with our own research ... growing spare organs in other animals ). Another idea: they talk about "Light speed travel with downsides." Perhaps the 'downside' is you lose altruism with what you leave behind - you can't trade or establish symbiotic relationships over excessive distances. this will sound convoluted but... You could make a round trip, with time dilation. [1]start on a planet 'A' , seed it in a way ready for step 3 [2] bugger off at near light speed to another 'B'. start on planet 'B'. do more of the same there.. [3] return to planet 'A', at near light speed. Steps 1-3 are 1 lifetime - ship time, but geological/evolutionary timescales planet time. The planet is now "ripe", so harvest it... by releasing the bio-engineering to transform it's biomass to your purposes. So perhaps the SJ's / Engineers have emerged from a process like this, imagine a species competing with itself doing this: e.g. some colonists set off, but you know that their descendants will be back with superior resources from un-populated planets ... so in the long run your gene pool is shafted unless you follow suit. Somewhere Ridley scott says something about "origins of mankind and what they must ultimately become" - i'm not suggesting that it's humans themselves that did this, just 'gaming' what the evolutionary incentive would become with space travel.