They seem quite useless in v5.0. Only use I've seen at all for them is removing destroyed AI mines on neutered AI worlds. The AI's remains rebuilders & engineers will repair the mines if left to their own devices so you'll need to kill them again but since I generally use decloakers with my fleets they're a minor annoyance for me.
In a related note, why does the AI have so many remains rebuilders around it's command stations? I end up with dozens of reclaimed ones even when I have Leech SS as my only reclamator ships. Even in systems with no mines there's usually at least a couple of them doing absolutely nothing. Actually I'll go mantis this as it seems a bit pointless.
