Captain Dart
In the rest of the world the response is just callsign, and if you are a polite pilot, 'thank you'. If the clearance is 'cleared only 20 miles right' or similar, yes, you would read that back because it is different to what you asked for. With ADS and radar I really don't see the big deal.
Surveillance certainly makes a difference to the 'effect' of a WX/any diversion from planned/cleared track/course; but I would want a readback - confirmation that you understood how much leverage you had; even in my full radar (non Oz) environment; it's about knowing how many other sectors/units you are plowing into; it's not just initial separation, we do more coordination with other units with diversions than at any other time. Also the 'readback' would assist that 'journalising' didn't occur at either end of the mic.
As for getting 'pinged' for being offset I suspect it's all in the manner in which the aircraft offset itself (or you offset it), a 20+ degree turn to do it fast could be a big deal; where as a gentle 5 degree turn to achieve it would hardly be noticed. I certainly wouldn't be able to tell if you were 1NM offset on my equipment in Enroute. Also it depends on the environment, if you are in or approaching the TMA a 1NM offset is a big deal (the SID/STAR integration doesn't account for offsets), where as at cruise in the middle of NSW it would be really no big deal.