We didn't stay for the dancing/nightclub so just reviewing Vivaz as a place to eat.
Ambience is generally a bit tired although if you are lucky enough to get a table near the windows then there are some quite good views of the Harbour and Opera House. We liked that the tables are well spaced but later on when they turned the music up (after about 9:15pm) then it got quite noisy for conversation.
Food is fairly basic, served canteen style i.e. they let you know that the food is now on and you form a line and shuffle past the counters selecting what you want until you get to the grill station at the end and are served a choice of pork, beef, chicken wings and chorizo. If you want seconds of something you stand in the line again. This did break down a bit towards the end and you could go and help yourself buffet style but the way it is organised and laid out tends to make people form a queue. Not really our thing. The refresh rate on the serve yourself dishes was poor so that when going back for seconds or some bread, lots was missing (although eventually they did replenish everything).
The meat was nice - well cooked and spiced, particularly the pork belly. With the exception of a couple of vaguely South American dishes (such as roasted peppers) the vegetables and salads were mostly fairly basic, a couple of different potato salads, a couple of different pasta salads, beetroot, tomato, green salad, cauliflower etc. The sort of stuff that you might see in a cheap hotel or a canteen of some sort.
Staffing was minimal. We ended up just about crash tackling a waitress to order a bottle of wine (although the list was quite reasonable as to quality and price) and then it took ten minutes for her to come back and tell us that they had run out of our selection.
We think that there are many better options in Sydney for this style of food but there probably aren't any cheaper ones, certainly not in town. Vivaz also runs lots of specials via the Groupon style buying services that make it even cheaper. That would be pretty much its major attraction.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.