Try looking above and/or below the ecliptic. Why? Since the bulk of the solar
system's matter appears to reside in the ecliptic, logically any species
that is starting to explore their solar system isn't going to take much
notice of the 'basically' empty space. Of course they'll be interested in
anything outside of the ecliptic, if only to be sure it isn't likely to
impact their planet, but, if its not too odd, they'll largely ignore it.

They're going to be more interested in checking out the planets (and their
moons), especially if some of those planets/satellites are potentially
capable of supporting (or having done so) life.

Good idea. I think they would be very hard to find unless we could
detect the return signal.