To the experts on this subject: In what circumstances would flying one of these things on my property at or below eave hight, without my permission:
1/. Be lawful, or
2/. NOT constitute some form of trespass?
Surely no different to some scrote deciding to park uninvited in my driveway. Yes, it has happened... (Just because I am conveniently close to a major venue.)
Why wouldnt I have the right to take whatever action is necessary to 'impound' the thing and charge for its return, just as occurs with illegal parking?
The definition of 'populous area' is not clearly defined in the regulations, but I'm pretty sure it covers flying over the top of anyone's private property. It is not so clear what constitutes a 'populous area' when flying over something like a beach because it seems to be allowed depending upon how many people are using the beach, but it is not a good idea in my opinion to fly over the top of anyone, anytime, regardless.
I am not an expert in this matter and I refer you to section 101 volume 3 of the CASA regulations which covers this issue and you can judge for yourself.
I cannot comment on your right to impound a quadcopter, I have no idea, but damaging someone's property is as far as I am aware is deemed as malicious damage in one shape or another. That applies to any damage caused by the quadcopter as well. It is why there are such organisations as the MAAA which provides model aircraft club members with insurance.