I think we're overestimating ourselves here. Why would alien's advanced enough to reach us even bother with Earth?
Resources? No, there are countless other sources out there, other planets, moons and asteroids, from which a nomadic alien civilization could gather resources a lot quicker and easier than from Earth. Compared to other sources, Earth isn't a resource rich planet by any means.
Domination doesn't make any sense either. Why would they want to colonize Earth? All evidence is starting to point to Earth-type planets being somewhat common in the Universe, and you have to assume that there are plenty of other easier targets to colonize. Even then, just because our Earth supports us perfectly, doesn't mean it'll be nice and comfortable every other alien out there.
Humans and enslavement would be about the only unique resource Earth has to offer I think, but we're fragile organisms that need rest, food, can only work in certain specific environments and conditions, and are prone to violent uprisings when pinned down long enough. Again, you have to assume that an alien race floating around in space in giant ships would also have some pretty kickass machines happily doing all types of things for them in all types of environments and conditions.
In fact, about the only reason I can think of for an alien race to want to visit us would simply be for research and the knowledge gained. The exact same reason we visit other planets too.