Radio-Archaeology

[aramis]

I had not considered this but I don't think it would be significant. The Oort clouds would be more noticable if it interfered with light. There was some mention http://setifaq.org/faq.html#1.2.3 of interstellar plasma smearing the signal bandwidth. This was said to put a lower limit on the useful bandwidth of the reciever, but if it had any attenuating effect on the signal this was not mentioned.

My guess is that the space dust between here and Pluto would be every bit as disruptive to the signal as the space dust beyond.

Out to the heliopause, it's not dust; it's flowing plasma at near negligible densities. Past the heliopause, you actually get dust and gas. Again, at near negligible densities.