Ok, here is a way that you can add some repeatable variable missions to the game without VO requirement.
You have plenty of mission terminals throughout the game. You also have a holocommunicator, and I am going to suggest something similar for personal use.
I would suggest you add a mission generator, one that will spawn certain mobs in a specific area on a planet, with a minor boss character using a summon trigger. The idea is that you would click on the mission terminal, and missions would be listed for you to choose from. The mobs and mini-boss would be randomly generated but level specific to the planet of course.
The mission can update using a "personal terminal" that lists text dialog...the idea is the missions are secret, so there is no vocal communication. Text is received to keep the communication completely secure.
Call them spec op missions or something to that effect, and they would be specific to your class and offer class based drops equal to general drops from the regular world.
You can offer different scenarios...vs 6 plus boss, 8 plus boss, 4/4 plus boss, 6/6/6 and objective, etc. Try to avoid gather quests as those tend to be pretty boring, as well as animal missions (unless you want to offer profession specific missions).
This is a way to offer reasonable content as far as development cost, and gives some variety and filler on the planets.
The main goal is to provide the generated content without requiring VO...
...now if you guys are slick, you could pull some of the voice work already in the game, like certain general responses and the like, as well as alien dialog (after all, any words can be attributed to alien dialog) to allow conversation choices in this generated content. I think generated content with at least one short conversation would be a home run.
This also, in the future, could be the basis for a mission editor/mission creation system for players.
Not a bad idea i like it