There has been some reports on TA of guests not being happy with the dinner show,and quite a few expressed their disappointment with the cost.
I guess, everyone has different expectations.
I can't comment on the dinner show as I've never been and never intend to go,as it'snot my interest, but everyone is different.
I hope you get a few more replies from previous visitors regarding this.
In the meantime,my suggestions is, if unsure, don't go,as it is rather pricey. You can just go during the day and experience their culture,dance,boomerang/spear throwing, didgeridoo playing and more. They will pick up from your accommodation,and you can book direct with them.
Their website is http://www.tjapukai.com.au/
if not having lunch there I would allow at least a couple of hours, but have a look at what they offer and times that the shows are on and this will help you decide how long to spend there.