To suggest that the variety of life forms that are possible is some kind of evidence that we can't have been visited by life forms that are similar to us is more an act of faith than logical reasoning.

As has been said before, just because there is probably an infinite number of possible life forms, that doesn't mean that there can't be similar life forms (lots of them), and if there are, it only makes sense that the ones who seek us out would be similar to us.