If I were an Ambassador elite guest staying regularly at a Sydney hotel that hasn’t ever upgraded me to a suite despite low occupancy and plentiful availability of suites, like the OP indicates, I would seriously question how that property really values my loyalty. I doubt I would continue staying at that hotel.

And if I were to continue staying at that hotel, then I’d clearly be sending the message that such behavior is acceptable to me. So it seems superfluous IMO to complain about that which has been accepted.

That’s never happened to me. Never. I’m an Ambassador guest in N America, supposedly the place where loyalty and elite recognition are consistently inferior to Asia/Pacific. Yet every hotel at which I’m a repeat guest—and I do mean every single one—I’ve been consistently if not always upgraded to a suite. (OK, the exception is the crappy Sheraton Times Square, but I’ve only stayed there with a group and never on my own.)