I have the feeling that more things must be possible to do with planetary tiles. Right now (playing as the Onyx and nothing else since Crusade, so I have only a limited view 
) I always start colonizing a planet by building Deep Core Mine, Space Elevator and Starport in this order, what does not really require decision making on my part ...
So I came up with some ideas to make planetary exploitation more interesting (and that normally need some tech advancement to be available):
- New improvement Think Tank: research building that increases the chance for a random breakthrough (player gets tech in the currently researched branch, but not necessarily the tech they currently research, but chosen from a pool of two levels above current tech level, and including any not taken specialisations). Colony unique, adjacency bonus +1 research. Chance to get a breakthrough is calculated by 1 - 0.995^x with x being the number of Think Tanks throughout the empire (factor 0.995 may have to be balanced by map size). Receiving adjacency bonuses from adjacent research buildings give +5% research on that planet per level.
- Military Factory: converts social production to military (ship) production, base value 10%, increased by adjacent social or all production improvements by 5% per level. Colony unique, gives +1 ship production adjacency bonus.
- Scrap Farm: converts military (ship) production to social production (with which projects can be carried out when planet is full, so don't underestimate social production ), base value 10%, increased by adjacent military (ship) or all production improvements by 5% per level. Colony unique, gives +1 social production adjacency bonus.
- Improve Tile project: after the build time gives you a % chance to transform the tile into one with adjacency bonuses (random? specific?). Can only be started on empty tiles.
- Introduce new planetary trait: Archaelogical Site. That would allow an Excavation project which gives the player after the build time a % chance for a special ship (but please don't restict it to the current tech level of the player like the ships you can get by planetary events that say something like "advanced precursor vessel") or a random, even very advanced, possibly unique and not otherwise aquirable tech.
- New Terraforming project: as far as I understand the current terraforming mechanic planetary tiles are given a "difficulty" that make them available for terraforming dependent on terraforming tecjh level. I want to introduce a new terraforming project that can be executed on any tile and give the player after the build time a % chance reverse proportional to the tile difficulty to terraform the tile.
- Exploit tile project: executable on any empty tile with adjacency bonuses, after the build time it removes the bonus but gives a huge profit, eg. 5000 credits per bonus point for removal of a wealth bonus tile or 500 research points per bonus point for removal of a research bonus tile. The adjacency bonuses would disappear also, the tile would be a perfectly normal one after the operation.
One side idea not directly related to improvements: Influence has not enough impact atm imo. To improve that a bit make influence increase tourism income (say by 10% per 100 points of influence).
I just started, so I will add to this post when I have further ideas.
