The rules for influence victory have changed, in case no one has noticed since the early versions.
Now, influence (for an influence victory) is determined on territory owned, not influence points. So you actually have to conquer several races to achieve it. It is just short of a conquest victory, and when you control more than 75% of the galaxy.
I had a game where I had 3 influence resources and all the influence improvements and bonuses. On the graph I had like 90%, but in the Victory screen I only had about 30%. I had to take over several to gain enough planets to achieve 75% control.
And as it is now, I do not see how a conquest victory is even possible any more. If two races each own half the galaxy, and I decide to take the other by conquest, I will achieve influence victory conditions before I can complete the conquest. I guess the influence victory option has to be turned off at the game start to do it. A choice of one or the other.