Sadly there's so many hoaxes out there that if there's any REAL evidence, it gets painted with the same broad DUBIOUS brush.
Of course I believe that there is life, intelligent life, in the universe.
As to whether it has visited Earth?
Well maybe.
But to be perfetly honest give the distances between stars I'd be AS inclined to believe that TIME TRAVELORS are visiting us as ALIENS.
After all, it seems likely that if one can travel between the stars one will likely have also found a way to beat the clock.
Einstein proved that time travel was theoretically possible and that our concept of time via the clock would accommodate it. But then again, if you are religious, it is logical that the God who is author of it all, including time and space, would not be constrained by the same 'clock' that is imposed on us mere mortals.
But even if we go with our more mundane concept of physics, is the possibility of hyper-warp speeds so impossible? Is that any more implausible to us than a concept of mach speeds would have been to those traversing the country in Conestoga wagons?
Two of my favorite movies provide food for thought. One Spielberg movie "Always" has the newly deceased character played by Richard Dreyfus receiving preliminary instructions from an experienced guiding angel, and as they move from place to place, the time frame shifts. She explains "Time is funny stuff, Pete."
The other "Final Countdown" is a decent sci-fi flick in which the concept is the aircraft carrier Nimitz at sea in 1981 passing through a time warp and finding itself in 1941 shortly before Japan bombed Pearl Harbor. The Nimitz alone had the fire power to destroy the entire Japanese fleet and the plot was in part the decision of whether to do that and thereby alter history and what the ramifications of that would be.
But the most interesting thing was:
1. Mr. Tideman, the contractor who designed the Nimitz, sees his employee, Warren Lasky, an efficiency expert, off at Pearl Harbor. Lasky is flown to the Nimitz as it embarks on some routine maneuvers. Lasky has never met Mr. Tideman.
2. On board the Nimitz, Lasky meets Commander Owens, the chief pilot in charge of air operations.
3. Just before the Nimitz can effect an attack on the Japanese fleet, the time warp reclaims the Nimitz and returns it to the 20th Century. Due to a plot twist, Commander Owen is left behind in 1941.
4. As Lasky leaves the Nimitz he is greeted by Mr. Tideman who now invites him into his Limousine and Lasky discovers that Mr. Tideman is Commander Owen who is now 40 years older.
So okay, you can think of how advantageous it would be to us to be able to go back 40 years and relive them with the knowledge we have now. But also, Owens/Tideman also existed simultaneously as the 30 something year old Owens and as the 70 something year old Tideman. And it is that I can't quite wrap my mind around in the concept of time travel.