Side issue, but if you don't care about travel time, you also have another big problem. The frequency with which stuff happens that matters to civilizations has increased significantly over time. Meaning that the time intervals that matter have gone down a LOT as we've evolved and that seems like a natural tendency on the basis of natural selection: higher frequency strategies will tend to dominate. So then you have this massive juxtaposition between probe travel times and things civilizations care about. It's a total mismatch. By the time the probe reaches its destination and can come back, the civilization will likely have completely changed and/or forgotten about it.