Well they said there would be rare stuff, they didn't say they would be super powerful and let you "start stomping everything on the map". There are plenty of rare and interesting events in Galactic Civilizations, but while they might cause you to change your gameplay, they generally don't cause you to win or lose because of one thing.
This is true. The main example I like to give in Elemental's case is when Frogboy talked about the "Diamond Golem Quest" that would only appear once every 400 games. I don't know if that's something that's in game for certain or if he was just using it as an example, but I use his example as my example. IIRC what he said about it was that it would be a multi-part quest and there's not even a guarantee the player would be able to finish the quest and get the Golem without interference from one of the other factions in game. There are many many factors to overcome in getting the quest and getting all the items you need to make the Golem, but once you (or the AI) gets the Golem...watch the hell out...LoL. It would be the real life equivalent of one nation on Earth having an Atomic Bomb while everyone else is using guns and small arms fire.
It definitely Would unbalance the game, but, that's the point and half the fun of it. Keeping it Very Rare is what makes it fun because you Won't have something that drastically unbalances the game there very often. Just the "chance" of something like that happening brings a lot to the table for a single player game. Imagine if you're loosing the game, badly, and then you stumble on the quest to get the Diamond Golem. Completing that quest and getting the Golem could turn a loosing game into a winning game And it would be a challenge to finish the quest and get the Golem before you're wiped out of existence. As long as it's limited and doesn't happen very often I don't see any problems with it at all. No one can expect to win all the time and no one should expect to loose all the time.
One of the things with long played out strategy games though is there comes a point in every game that's played where you either know you're going to win, or you're going to loose. Often this knowledge comes at Mid to Late game. Imagine you've hit that point, you know you're going to win, you have 5 massive "stacks of doom" heading to finish off the capitols of your enemies, and then one of those enemies gets the Diamond Golem. Now you're forced to turn all 5 of those stacks of doom against the Diamond Golem to stop it from crushing your cities. You succeed but take heavy losses. Now the other factions on the map have a fighting chance again and you Don't know for certain that you're going to win anymore. I don't know about you, but to me that sounds like a Bad Ass Game . Just the chance of things like that happening that can turn the tables on a winning or loosing game means that it's worth it to play out each game from it's start to the bitter end. This is something all deep and engrossing strategy games should strive for and I think for once Elemental is going to break the trend in strategy gaming where you often know whether you'll win or loose.