In general I'd suggest reading "The player of Games" by Banks.
A Culture novel that explores why would someone care about being good at "boardgames" in a universe where even the dumbest appliance could easily outperform any human.
Humanity has very limited purpose in the Culture. On the surface, it looks nice, but they're effectively pets. Their willingness to ascend was cut off right along with their willingness to live.
All of which is done by social engineering. If you want to go the intelligence-enhancement route, they'll help. They just make sure that very few people do.
And dying is just one of several end-of-life events you can pick, if you want to (including opting out entirely). Naturally it's the one we tend to focus on, because it's the only one we currently have, but the Culture's got lots.
What are the negative effects of having more Minds? Resource depletion?
If your cat suddenly tells you that what it wants more than anything is to learn General Relativity, then either you're having a psychotic episode, or you have to question how benevolent and ethical your coddling is for your fuzzy wuzzy slave animal.
It's also mentioned that you can have your mind transferred into a drone busy, and vice versa, but it's seen as terribly gauche.
The manners as laws thing is cute, but I don't see it working without invasive non-consensual modification of humans.
E.g. from my own perspective, if I live in a world where there are humans and human-created demigods, then obviously I want to be one of the demigods. Not to enslave the humans, but to look inside of black holes, to travel between stars, to fully understand how biology works, etc.
So not everyone wants to be a scientist or engineer, but wouldn't almost all engineers and scientists want to wield the very best mental and technological tools of their civilization?