In my second-most-recent game I conquered a couple minor planets, both of them fairly high quality. I had about 30 tiles to use, in all. I had no real use for these planets since I was already right where I wanted to be in the game, so I decided to use them to maybe flip a nearby enemy world. I filled them with nothing but influence structures, and rush-built as many as I could.

In a span of 50 turns at the most I went from "doing good", to "everyone is helpless at my feet begging for mercy". Why? Because my tourism income had just more than doubled my tax income - as in, my tax brought in about 1000, and my tourism, formerly at about 215, was over 2000. Suddenly I could basically do without ANY taxation of any kind, planets were rebelling on all sides, my ships with "+25% to attack in own space" modules were all but invincible pretty much anywhere (as my influence now covered more than half the map, originally being less than 1/8th), and I was able to rush-build a 3,000 bc ship every second turn and still have a surplus.

I did not have restaurant of eternity or any other remarkable influence structures, I was only one or two techs into the culture tree, and no random events happened. I was playing one difficulty level below "tough". I've since duplicated this in my most recent game, so it's not a one-off.

Does this seem a little overpowered to anyone?  To me it seems like there must be a math bug somewhere, since, after all, had I built nothing but economic structures on those planets, I would have had nowhere near this level of economic bonus, nor would I have had any of the other benefits (flipping planets, etc).  Now I know all I have to do is conquer a decent planet somewhere near the middle of the map, and I'll instantly have all but won the game.