Life itself is a very selfish "Force". All life wants is more, is something in return. Life thrives on receiving, everything we do is for ourselves. We give money to a friend expecting a thanks, credit, and if you dont receive it you get upset. You try and get that job so you get paid, if you dont get paid you get upset. You turn on the TV to be entertained, if you're not entertained, you get upset.
So with this said, If an alien species came to earth, this automatically tells us they're far more advanced then we are because they're able to travel and sustain their species through long travels in space. So, this means we have nothing they'll want when it comes to intelligence, so what else would they want? Well, our resources.
But then, if you think about it, the basic resources like water, fuel, etc is all over the galaxy, in every solar system, there are many different types of resources. So, this being the case why would an advanced alien species purposely destroy our planet, the species on it for a bit of resource they can get from Europa, Jupiter, the moon, mars etc?
I personally don't think an Alien species will take the resources off our planet, specially at their level of intelligence. The only thing I can see them doing is using us for experimentation or as something else. Not as slaves, because again, at their level of intelligence one would expect them to already mastered AI, robotics can do work much more efficiently and quickly as us.
So, again, with all this said... would they even bother with us? We have nothing to offer them at all.