I felt like Null-A wasn't so much a political philosophy as it as a superpower. Like, while Dune is obviously about politics, it would be much less so if it was about Prana-Bindu. The Spice, Prana-Bindu, and so forth are setting material that orbit analogues for real-world phenomena like the Turkish empire, oil monopoly, and religious fanaticism. I consider The World of Null-A to be a more psychedelic experiment, where the political considerations are loosely sketched in, and it orbits the world in which the Null-A philosophy gives people superpowers.I'd second Morgan, Heinlein and LeGuin, and considering the OP's handle I assume you've read the Foundation series? Not to everyone's taste (I am not a fan for instance) but certainly a good fit with your criteria. Null-A by Van Vogt could also be an option - political system in casu "non-Aristotelian logic".
Foundation is neat because every story discusses a different sociopolitical order. It's one of the big influences on Shock:Human Contact for that reason.
Heinlein's a good call. While I first thought of Stranger in a Strange Land (not at all space opera, Asimovking), Starship Troopers is an exploration of what a warrior society might look like, how it benefits, and what it costs its members.