They do seem pretty random (Distress Call Threat 0). In War USS they tend to want repairing, otherwise they want fueling. Some of the repairs too several limpets - they seem to need to get to > 20% repaired (need more data). Had one which seemed empty, haven't see the one with wreckage yet.
They could be quite fun if you fancy a bit of Search+Rescue RP, but there are several issues:
* USS spawn rate - they seem to seen specific system states and you still don't get many
* USS spawn location - whoever thought USSs spawning 10k+ ls away is fun was a masochist
* Payout - 2500 CR for 10 minutes travel? Oh, maybe they put rare encoded mats on the wake of the rescued ship? Nope, G1
* Build - you want repair and refuel limpets, neither of which is a common choice in many builds
I reckon if fdev fixed any three of these I could ignore the other, but as they stand I doubt I'll be off on search+rescue missions for a while
Edit: And then I went to Epsilon Eridani as apparently it is a HGE hotspot - zero NHS, a ton of distress calls. Ah ED