I'd say given the vastness of the universe, that it is ignorant to assume that our planet is the only planet that has life. As for intelligent life out there, past or present, odds are low based on our observations, but until we have a better answer than "infinite" for "how big is our universe" there exists a probability simply because of our existence being a proof.

Now whether or not a flying tophat, or two saucers stacked upside down have visited us, I'm on the skeptical side of the fence.

Now don't get me down the alternate dimensions/multiverse rabbit hole, because you did not get them all!