Assuming of course that there is no planet within shorter range than you imagine which can sustain life.
They may also live much longer than us so travelling for longer isn't such an issue.
Perhaps they could use wormholes to shorten the journey.
Perhaps time moves much slower for them so the journey appears shorter than it would be for us.
'Given what we know' could be very limited in comparison to them if they are vastly superior.
All possible, but some of them quite unlikely. We know the theory behind creating wormholes, for example, but the require vasts amount of energy. Energy we would detect if another race created them.
Time does move slower near the speed of light but not nearly enough to make a difference. At 95% the speed of light time dialates by only 30%. That means the nearest star is still almost 3 light years away.
You are right that an alien species wouldn't have to be much more intelligent to make a huge difference, compare a chimp with a human for example. Chimps have an estimated iq of 65-75 where an averrage human is 100. Those few points make a big difference. It is very possible that an alien craft passed the hubble telescope and they all pointed and went, look they have a telescope, how quaint.
All that said, most cosmologists estimate that there may be very few intelligent civilizations in the galaxy, some even think it is very unlikely there are any. Add that that to the vast distances and the chances of us being visited by an intelligent alien life is tiny.
As for eye witness testimony there are lots of examples of convincing stories that turned out to have a logical explanation. It is not accidental that cosmologists, bioth amatuer and proffessional do not report UFO sightings. Why? Because they generally know what they are looking at.
The state trooper that said he saw a light in the sky zigzagging, for example. Turned out he was looking at venus and he was on a winding road.