[Tyneras]

Venus might work as an Africa analog, with various swamps and dense jungles and maybe a few inland savannas. Instead of just once race, why not multiple frog and reptile tribes/species that the humans play against one another. Plus who knows what horrible beasts lurking in the shadows.

A pulp mars has several possibilities, but I favor the almost extinct martians and your "Martian Inoculation" idea. If it's a self reproducing symbiotic bacteria spys would only need to steal it once for everyone to get it.

If the Martians are treated more like "wise old foreign elders" rather than someone to be conquered I can just imagine the tales those martians might spin of old treasures and technology lost under the advancing sands. Plus the last of the Martian cities might just be too heavily armed and armored to bother with considering there's a whole planet to explore.