Some data points from my first OZ flights (i've been an Oz member for few years and am on the way to lifetime D+ status:

LHR-SYD moved from economy to economy smartium on check-in (full flight)
ICN-SYD no noticeable extra benefits
SYD-ICN blocked seat next to me (this was confirmed at check-in), and the senior cabin crew member thanked me for flying OZ
ICN-LHR the empty two seats in my row of 3 were marked 'Do Not Occupy' by cabin crew (the only seats not in smartium to be so marked) and cabin crew took a lot of care to check I was ok for drinks etc

So it seems there are some benefits of D+.

I wasn't impressed with the lounge at ICN (business central) - overcrowded and with a poor food and drinks selection and a poor layout with the food at one end and the drinks at the other. The food was the same both times through the lounge in two weeks and not that great.

Priority boarding worked well, service and food on board was good.

As shame the bonus miles for flying OZ with status don't count for lifetime status!