Interstellar travel takes a huge amount of time and energy. Assuming sufficiently advanced aliens exist, they would have to have a very good reason to spend the time and energy coming here. They also may not be capable of surviving in our gravity or our atmosphere. In addition, being exposed to an alien ecology would be extremely dangerous, for us as well as them.
The most likely reason I can think of for aliens to visit our solar system is to harvest the Sun. I personally hope there is no civilisation in the universe that is more advanced than ours.