What would be the point in a self-replicating wave of expansion? I don't see why that would make life more enjoyable. Unless that wave is used as a discovery machine - in that case it's a scientific tool, and as scientists we have rules about interacting with other species, conservation, etc. I'm sure if these aliens exist they have reasons for deliberately not devouring our galaxy, and we'll know those reasons as soon as we are able to launch a self-replicating wave of expansion.