Unlike crewed spacecraft, automated probes would be a viable means of extending a civilization's reach outside of its own solar system with minimal expense or risk. Our own civilization has already sent two probes into interplantary space.
Probes also improve on two of the challenges of optical, radio and other forms of information-only broadcast: they're cheap when compared with the cost of constantly powering a signal beacon, and if augmented with some level of autonomous AI can be a much more responsive communications channel than long distance speed-of-light communication.
