I am with you on an expectation that the morphology of sentient biological-esque creatures across the cosmos would reflect a wider range of body types based on influences from local environments, far more so than Star Trek depicts. One thing I think is crucial about any life form that does a similar thing to what we do is some kind of hand or other type tool appendage(s) as a means to develop the kind of refined builder manipulator status we have to harness the otherwise capricious tides of nature. To put it glibly, dolphins need better hands to cross the bridge to civilized society, so would any alien. Perhaps a more steady planet would produce a dodo bird like creature, less able to adapt because of the lack of need, but perhaps social and conscious... I don't know. I think it would be interesting to unpack the possibilities along those multi variate lines. Perhaps symbiotic entanglements between dovetailed functional interdependent systems, compartmentalized activities that work together without necessarily understanding their participation in the full picture. Emergent traits based on that model seem to be the norm in nature from microbes to ants to cells and organs in humans, to humans as part of larger systems. For instance, we don't know if our cognitive functions might not be part of a present means to release carbon and a future species apoptosis function once we sufficiently released the carbon for recycling onto the larger bio-economy. That may be a dead end speculation, but my point is nature appears to have these perspicacious schemes embedded in the function all the time, by what means I am not sure.
On the morphology of the culture environment dance; I think Jared Diamond is on to something, as are people like Marvin Harris who drew a connection between abstract cultural maps and environment. I see influences from things like harsher climates, the necessity to hunt, along with the level of difficulty and reliability of the hunt and things like seasons that required temporal planning and so on when compared to picking fruit off trees as factors in the development of both behaviors and the corresponding abstract value structures which would mimic those realities in token form. Exposure to droughts, climate changes, the need to adapt are all reflected there in culture. To Jared's point, the hunter-explorer-conqueror-empire builder connection might come from a co-opted branches that grew out of those necessities. It seems the most plausible explanation to me. I also think the parasite-stress hypothesis is worth unpacking more than it has been to see where it leads.
I did see that paper on plate tectonic movement once and was fascinated. Then I lost track of where it was. Do you have a reference, I'd like to revisit it. I think things like coral reefs that can have a stabilizing effect on shorelines which in turn helps them and the like are threaded throughout the biological economy. I do not see why it would not extend to plate tectonics. Microbes certainly drove Earth's mineral evolution on which further biological possibilities were born, not the least of which is the emergence of gum chewing O2 converting glorified dung beetles that we happen to be. :)
One note on written language. I think, like the case of the allele that prevents malaria also causes sickle cell anemia when it is passed on from both parental lineages, writing comes with benefits and costs. On the cost side, I think writing has preserved certain ideas long past their useful shelf life. Stories once told by the fireside that served as a means for cultures to navigate the realities they existed in in the past would also morph over time to keep pace with shifting social environmental conditions, but are sometimes used longer than their "sell-by" date as a result of that powerful technology to conserve information.