The Expanse had its finale on Amazon Prime this week. Its rocket-propelled space battles, intrasolar system conflict, and relative paucity of AI, cyber-, or bio- tech got me thinking about science fiction of the Golden Age and the pulps. I think you could fairly easily transplant much of the conflict and setting of the series to a setting with gleaming-hulled rockets, habitable planets beyond Earth, and 50s haircuts. That last one is optional.
There are different approaches to take, of course. You could go full Captain Future with every celestial body in the system with enough gravity to be spheroid having native human life, or something more like the work of Stanley Weinbaum where the other worlds are not so hospitable to humans and the life there is alien. I think a Weinbaum approach would fit well with the protomolecule and ring gate stuff, but that material is less interesting to me that the human-colonized solar system conflict. My approach would be something along the lines of Asimov's Lucky Starr juveniles or some 50s work of Poul Anderson: a view of the planets that proved to inaccurate, but was plausible (if optimistic) at the time the stories were written.
So the settled inner worlds would include Earth, Mars, and Venus. Venus would be a water world, perhaps with artificial islands or undersea cities. Mercury would likely research stations or the like, controlled by the UN on Earth. Unlike in The Expanse, Mars and Venus would likely have native life, though probably not intelligent life.
The Belt would be much like in the show, though in keeping with pulp conventions, pirates would be more common. The Outer moons might be a bit more hospitable (perhaps a lot more depending on how pulp you want to get) so the Outers as a whole group might be a bit better off than in The Expanse.
What does this add? Well, it certainly adds a new aesthetic. And of course, since this becomes alternate history, so you've got the potential for it to go in a very different direction from similar core conceits and concepts.