I don’t have the expansion, yet. Will someone explain what advantage there is in raising the Venusian rating (other than the obvious TR bonus I assume you’ll get) versus raising a Martian parameter or other action? For example, why not spend money on a greenery tile which may yield more VP at game end than 15M€ for a Venusian parameter?
Like everything else it depends on circumstances.
Maybe you increase Venus to take advantage of a bonus on that track.
Maybe you have a card that has a requirement for Venus to be at a particular level.
Maybe you don't want to set some other player up to gain a bonus on another track.
Maybe you have a card that increases Venus bu no card to increase another parameter.
I'm sure others can come up with other reasons.