One thing I noticed while playing is that Tropicans more or less pick their factions at random on a bell curve. It would create more meaningful decisions if a Tropican's faction choice was influenced by factors like their wealth, occupation, education level, and specific happiness needs.

For instance, soldiers might be more likely to join the militarist faction. Low relations with superpowers or high rebel threat might also influence Tropicans to want a stronger military. The broke and poor might be more inclined towards communism, while the well-off and rich would support capitalism. Maybe high religious satisfaction makes Tropicans more likely to support the religious faction. College educated people might be more likely to be members of the intellectual faction.

This would give a lot of ability to control faction choice outside of propaganda, if you are willing to make the appropriate tradeoffs.

This would also need a lot of balancing to fit with the other systems of the game as well.