Mhen'ga: Vanae Spears are very valuable, but no one on Mhen'ga will buy them for anywhere near their full value. Store any you get for later. Make sure to sell any Zil Rations and Honey to Burt at his Mead Hall. The're worth 0 credits anywhere else.
Tarkus: Go to the Western side of the map (near the Stellar Tether). Sex Bots drop 'Hammer' Shield Belts and you can get a Vial of Microbots from each Goo Girl if you have high Intelligence or are a Tech Specialist. Any enemy can drop Slutshrooms, Motherhusks or Spunkshrooms depending on your genitals, all of which are valuable. Recruiting Anno is a good idea because she'll buy anything for 90% if she's on your crew. When she's working in the shop she has a much more limited list of item types she'll buy. Giving Shekka the Probe makes you Nicer, but that's about it.
Myrellion: Bothriocs can drop some fairly valuable stuff, but there aren't really any majorly valuable drops from other enemy types. I wouldn't recommend farming here.
Uveto: If you want to bet on the Races, make sure to max Intelligence. Chance of winning seems to range from 1/3 to 2/3. You can find Savicite (12000 credits) out in the Tundra, and sometimes from enemies. Supposedly, equipping a Nog’wich Leash increases your chance: 1.33% -> 2.5%. All Korgonne can drop Yappi Straps and Insulated Coats. Female Korgonne can drop Crude Savicite Jewelry, which is moderately valuable. You can also find Lucinite (8000) in the Rift (the white squares).
Zheng Shi: The Mine is your best bet. Mining Robots are guaranteed to drop something and can drop all three crystals + Savicite. Bored Jumpers can drop Jumpsuits which are also valuable. Roz doesn't drop anything so steal her Power Armor even if you don't want to actually use it. If/when you defeat Overseer Maike don't free the slaves. That dilutes the encounter pool with slave orgies and Slavebreakers. If you're interested the Slavebreaker's Heavy Slut Ray, wait until you have All The Money. Then you can go back and free the slaves. Whatever you do, don't get the RFID badge from the Rodenian Mechanic. Also: Fighting the Bored Jumpers with a lot of Savicite in your inventory is much easier with an Airtight armor to block their Lust attack.
Depending on exactly what you want from Futazona, you could mix in some regular Amazona instead. They both count for the Overdose.