While I'm sure the probability of these sightings being aliens is actually extremely low there is nothing particularly surprising about them hiding from us. If they want to check us over to work out how to conquer us and colonise the planet its going to be subtle. The reality is they would likely send a very small team of aliens, handful to our system and then base themselves on another planet, Mars or further out seems likely. It's likely they would manufacture their required equipment in our system as well as develop biological weapons etc. The last thing they would want is to make their presence obvious so we start accelerating development and increasing our weapons. Life is all about resources and gathering them. Just sending a small craft between the stars takes huge energy and probably decades in transit. The idea of huge motherships coming is extremely unlikely.
We simply do not have enough information to form any real opinion on how much life is out there but recent developments have shown the existence of planets is extremely common and many found are in the goldie locks zone even for nearby stars. The chances of intelligent life elsewhere surely has increased with those discoveries. We really have no idea about such life though. Multi-cell lifeforms like us may be the rarity where as single cell life may be extremely common. Maybe if we survive long enough to see other stars ourselves we will discover a 100 worlds with single cell life for every multi-cell life planet and 20 extinct civilisations for every 1 still existing. As we develop more sophisticated communication equipment maybe we will discover signals that tell us where such life is. If their data rate is so huge compared to ours it will just appear as random background noise if they can transmit a gigabyte of data in the time it takes us to send and recognise a single bit. They may even be using other carrier systems. If you live in a cave which you have never left how could you predict what was outside?
That's what makes discoveries so exciting. We don't even know the majority of species on our own planet as most are undiscovered in the sea we mainly only know about the majority of life on the land and life that exists near the surface of the sea. Alien's that come to earth rarely with the intent of staying hidden just to take biological samples. It could be only 2 alien individuals that actually have to collect samples from just about every region on the planet and follow up samples etc. Not much opportunity to see them. Their intent may be to conquer and setup a colony within 300 years not 3 years.
