Outposts, as they are, add another layer of customization to your bases, however I believe that they could use improvement. No, I'm not talking about the ability to build facilities in outposts because I know that would be too awkward to implement since the buildings weren't designed for that purpose; I'm talking about simple upgrades to your outposts.
For example, you've just purchased an outpost that produces 1 food for your base every day for a cost of 300 influence: but for an additional 700 influence, the base can be upgraded to produce 2 food every day or maybe the upgrade could add another purpose to the outpost, like also providing two beds.
Of course, I could go on ,but you get the idea. It would add a whole new layer of depth to deciding what outposts you choose to claim and how your base is designed. I'm not sure if it would cause balancing issues, but as long as it's relatively expensive and only one or two upgrades can be used per outpost, then it would be a welcome addition without being unfair.