"but even that has a fairly short practical limit."
nope. Any signal that has ever broadcast anywhere and has had time to get here can be picked up, you just need a big enough antenna.
I did some research, and in order to pick up a TV level signal 100 light years away, we could built an antenna the size of Rhode Island in space.
That sound big, but if you could it out of small piece you can send and it can attach itself, we could do it for not much money every year. The great thing is we could just keep adding and get more and more 'fainter' signals.