Some of the examples you're quoting seem a bit odd. Many are focussed transmission, such as those to space probes, as opposed to the general unfocussed broadcasts from TV transmitters. Unless the aliens were in line with the focus area, they're even less likely to pick them up than the TV broadcasts. It'd be like trying to see a torch shining at an angle 90 degrees away from you, from 100 yards away. Others, such as GPS, are actually not very powerful, coming from orbital satellites as they are.
Seth's point is that the number of powerful general broadcast EM signals humanity produces is diminishing. So the point still stands - you'd need better than current human technology to find it.
SETI basically relies on an alien species pumping out a powerful signal aimed squarely at the Sol system, on the basis that a) their space telescopes and gravity wobble analysis have determined the existence of a rocky planet, with water, in the parent star's comfort zone; and b) we're in the correct time window to detect it.
Read the answer to the question
"Can you give some idea, in layman's terms, what kind of signals you could possibly detect, for example, how close would ET civilisations have to be in order for us to detect signals like TV transmissions?" on this SETI Q&A
My point about Voyager is not mistaken
, on my interpretation of your use of the word "practical". I was taking it as meaning "aliens who could
visit us to follow up on the EM signals, or vice versa". Human prospects for visiting other star systems are very dim at the moment.
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