I think adding some kind of airport would be nice.
As far as I understand planetary invasions (I might be wrong), you would attack after you destroyed enemy defence fleet. That leaves defenders without any ability of using fighters in ground combat (because they probably won't have any carriers nearby).
In VB you had PDC. Despite the fact, that fighters weren't able to support ground forces, you had possibility to launch them from a planet. My idea is the installation, that would be able to hold some fighter tonnage (for example 5000 tons per level/installation), perhaps giving researchable tonnage per level/installation increase, and allow to launch them. At the time, when fighters are on ground, the might not even be using MSP and won't be using maintenance facilities, because of that.
If someone suggested that earlier: I'm sorry. I'm simply too lazy to check for it in over 158 pages of posts.
I probably made a lot of grammar mistakes, so sorry for any of these.