Even if light speed was possible -(which is now generally accepted that it isnt) it would still take literally thousands of years to travel here from the nearest galaxy with what looks like a possibly habitable planet in it.
However, ignoring that little bump in the road - once they have completed this marathon journey - what do they do - keep themselves largely hidden for 70 + years - just taking the occasional cow, buzzing the military now and again and kidnapping the "odd" human.
Yep - i'm sold.
Maybe they can observe but cannot interact. Our understanding of space time and dimensions is pretty basic with so much unexplained. Perhaps they can harness time or dimensions in an unthinkable way, allowing travel at incredible speeds and maneuverability. Whilst they are visibly there, maybe they are not fully there so to speak. Could even be humans using this from the future which somehow silhouettes them into our time, but again cannot interact. Considering all the sightings over the years but never interactions makes you think they cannot for whatever reason. All sounds pretty crazy talk but who knows what is possible.