Earth may have resources that are "useful," however all the stuff we have on earth is found further out of the Sun's gravity well. Main belt asteroids have more heavy metals than earth, and you don't need to crawl out of a deep well to remove them from the solar system. And if you are only after water and gases, the oort cloud has more than enough that the cost to weight of getting the minuscule amount we have here on earth just isn't worth the energy. The ONLY reasons I can see for a hostile race to worry about humans is our technology (not likely if they are interstellar race), genetic mapping for bio war, to remove a possible future threat (the most probable reason I can think of) or, finally to colonize a planet in the "Goldie Locks zone." That last one has a lot of issues that may make it more beneficial to sterilize the planet due to biological contamination, and in that case mars would seem to be the better planet to transform IMHO.
In any other case I can think of, they would contact us and see what they could learn or teach us, or place a probe in the outer solar system to watch us. Not a lot of reason to worry about it all.
We get observed, first contact or death and there is nothing we can do to change it.