Crew members already have a class and rank, why not add level up mechanics to them to make them stronger and entice the player to train them up?
While their "level" scales with your armor, you can keep on "upgrading" yourself by many means (Augments, Vault Forge). It makes me feel like I'm leaving them behind after seeing them respawn in my ship after a hard session in the Ancient Vault with them. So yeah, I'm 100% for the idea to let a possibility for them to improve.
Yes, please! I'd love to take my Crew members to a planet just train them. It'd be really cool! Few features which could be added; A feature to select the type of armour they wear; Teach crew members to swim and make them follow us in liquids. A way to direct them where to gather in our ship, so they don't just go around running everywhere.
This can also apply to captured pets, I actually dont like the concept of "your armor determines their strength" thing