my personal opinion, which is based on many things including my friend's testimony, is that what we call aliens are really the nephilim. genetic, demonic concoctions. i think the abduction phenomenon is at least as much spiritual as it is physical if not more. i think that aliens will perpetuate the antichrist and false prophet, and the mark of the beast, which will be a genetic manipulation of some kind.
Anything is possible but aside from what you said it makes no sense for aliens jsut to come here to visit and fly around all these times and for so many years. If they were that advanced and if they were advanced enough to get here (which would be very advanced) they would be able to observe without being detected. UFO sightings started around the fifties...that is a very long time for them to just fly around. Could be possible just knowing all this doesnt seem likely.