Don't forget that the EME path loss includes reflection losses from the lunar surface! Current techniques permit us to detect fractional variations in the 3K background. HF attenuation depends on many factors including the state of the ionosphere and the horizon angle, and the distance at which they become undetectable in the 3K background (to our current technology) is frequency dependant. So I think you are overly pessimistic. However, the chances of a technological civilisation within the volume of space that our signals have travelled are quite slight...and I think it would be very sensible to detect them and learn as much as we can about them before we considered allowing them to detect us! Remember the conclusion of A. C. Clarkes short story "The Sentinal", the precursor of "2001".
Originally Posted by AF6LJ
"Only in silence the word, only in dark the light, only in dying life: bright the hawk's flight on the empty sky."