The universe is what, 15~20 BILLION years old. Our very own little planet is 4.5 BILLION years old. Yet humans, the ones we call "modern man" have only been walking this earth for some 70 thousand years (Mitochondrial Eve ).
But you're assuming (it seems to me) that other life would have the same developmental time lines as us.
But What if, their planet is say, .5~1 BILLION years older. What if their evolutionary development had tens (of thousands) or hundreds (of thousands), even a million years head start on us? Given the exponential rate of technological advancement we've seen in just the last 200 years here, what would a civilization be able to do with even just a thousand year head start?
As far as I'm concerned, we've only just begun to scratch the surface of science and physics and cosmology (et al). What we don't know could probably dwarf what we do know.
So, while I can understand our minds wanting to frame the discussion with a very human and Earth bound frame of reference, I don't consider it outside the realm of possibility that some ancient alien race has risen before us and has conquered far greater scientific challenges than we can now envision.
And who's to say whether or not some alien race just passing through our little backwater part of the Milky Way, didn't pick up on said radio signals, or, probably more of a signal like, uncontrolled nuclear fission (Trinity), taking place in our atmo, and take a detour to check it out.
Hey if it were me, I'd probably stop by to see what all the hub bub was about.
Nevertheless, there are still two things that stand out in my mind on the subject:
First, that the odds of actually being found by another civilization, no matter how advanced, are incredibly remote. Again, WE have only been producing signals that could be detected from a distance for 107 years. And again I assert that a sphere 107 light-years across is very, very small on a cosmic scale. The odds of an advanced species happening to be in the neighborhood to see/hear us are minimal. And I think you overestimate the detectibility of things like the Trinity test or any other nuclear explosion on earth, and like the radio signals, whatever aftereffects might have reached space can only have gone 63 light-years from here by now. It would be like sitting in a raft in the middle of the Pacific ocean, and just happening to be in the precise spot that a single grain of sand falling randomly from orbit struck the water. Even that analogy probably overstates the probability considerably.
Second, as someone else has pointed out, there are now thousands and thousands of cameras, many that take relatively good quality images, all over the planet. And yet, we still don't have much in the way of proof of any alien visitations.
I am not saying alien civilizations don't exist - given the size of the universe and the number of galaxies, solar systems, and planets, it seems far too likely that they do exist somewhere. All I am saying is that I do not believe for one second that any have ever visited, or are currently visiting, earth. And without solid, scientific, verifiable proof, I see no reason to believe those who insist that they are or have, particularly the "I was abducted by aliens" crowd.