I don't see anything particularly contradictory in what you say, EoS, since it is pretty much my own view. I certainly believe that thefts and break-ins happen to tourists and other travellers, but I have yet to come across any evidence that gas is involved. The fact that someone asserts 'I was gassed', does not prove that they were.
On the other hand we do not stay on motorway aires when we are on holiday, although we have done it a few times in the past. There are two reasons. Firstly, I do think it increases the risk of being a victim of crime, but more importantly, when we are on holiday, we like to enjoy every moment of the time, not just the bit in between the journey there and the journey back. By stopping off at proper campsites along the way, we can park the caravan in a spot which is likely to be more attractive than the busy parking area of an aire, then go off for a while to find a supermarket, a restaurant or just explore the local area. If we prefer, we can sit outside and relax with a drink, without the noise and fumes from other traffic disturbing us. We have spent many happy evenings in this way, and have often dicovered unknown areas to be returned to and explored properly at a later date.
I sympathise with those of you who arrive in the early hours and personally, in your circumstances, I would certainly look for an aire in which to get a few hours rest before travelling on. But, on the other hand, I avoid these night-time crossings like the plague: that is just not the way I want to start my holiday. Each to their own!