Wasn't quite sure where to post this, but it does seem to be a bit of a bug. The AI does not counter influence well enough. I still have to try it on intelligent, but even at lower levels the AI needs to do a bit more work to counter influence.
I had no influence resources, just one influence starbase (right next to my own homeplanets, mostly to counter potential enemy influence), I did have the galactic wonders for influence, but no more than one Embassy (and it's followups) per planet.
I built up a strong military to stop the AI from attacking me, and then just let the influence do its thing. I eventually started gaining so many planets I couldn't even keep up with keeping them all properly built and defended. One turn I gained THREE new planets due to influence.
I love the influence part of the game, but it seems that every game I play, I can win through influence without even trying. An influence victory should be a dedicated effort to spread your influence, not just grabbing a few planets and building an embassy on each one, building two galactic wonders and voila, you've got 75% influence. But because the AI doesn't counter you, that does seem to be what happens.
I now play with the influence victory turned off, because it happens too quickly. By the time I finally get a neat empire going, the entire galaxy eats at my burger joints...
It shouldn't be that it becomes impossible to win through influence, but I think that if you want to get an influence victory, you should really have to work at it. Right now it just sorta happens.
Hope this helps somehow.
Creston