Too Many Earths To Visit
Unlike the theory located in this Thread: The Earth Is So Unique, it could be in a universe of billions of planets that superior alien life is aware of so many earths like this one that it makes ours just 'another' to visit one day - in other words we're not as special as we think we are. This may be the reason why Directly Meeting With Aliens has not happened yet.
I would think most would observe us first, unless they wanted the resources we have. After observing us, they would just leave.
There are planets that rain diamonds while others may hold gas in the atmosphere that act as the most powerful fuels in the universe. Considering that, 'little' earth is just a wasted visit really probably more so because they would have to deal with primitive earthlings.