Interstellar transmissions would be broadcast at light speed only during the brief 50-100 year period between development of radio technology and its replacement by faster-than-light (FTL) communication. The chance that we might detect radio transmissions depends on our pointing a receiver at a civilization which was exactly at that brief stage of radio use when the signal was sent. This chance is very small, but, in my opinion, still quite worth trying.
We ourselves are likely immersed in FTL
transmissions from more advanced civilizations, unaware of them for simple lack
of the technology to build a receiver. The exciting thing about FTL communication is that it will give us access to the "Encyclopedia Galactica" and all the knowledge that countless advanced civilizations have chosen to give us.