First, I wouldn't say we are looking for intelligent life, because it's clear that there isn't any in our solar system and we can't really look beyond our solar system. We are looking for life, ie, bacteria, because that would at least prove that there is life beyond earth, but if scientists found out that this bacteria is identical to bacteria on Earth, then we would lose interest in it, faster than we did the moon.
Now, onto you reasons, none of them make sense. Any civilization that can get here, would obviously have weapons that we couldn't compete against, thus if they were looking for a place to live, we would know, because we wouldn't be living here. Same applies for resources, but if would have to be one hell of a resource, because the resources needed to make this journey, would still be astronomical.
Us being an experiment, is just way too cartoonish to make sense. Not because we humans hold any special significance on a cosmic level, but simply because we're too far away to be of any interest. We're not talking about driving down town to the aquarium or the zoo, we're talking going at minimum 16 light years. And if life exists on several planets, why would a civilization that can't even land on Mars, the next closest planet, be of any significance to them?