I pretty much agree with all this about Rua. Except this trip is on the cusp of NZ school hols and Ruapehu will be carnage. I think for this family Queenstown may well be a better option, riding at Cardrona and Remarks. The suggestion in the thread to stay at The Sherwood is a good one, if you don't want to drive up the hill every day the bus will stop right by there on Frankton Road.
Having just got back from Queenstown and Wanaka. Queenstown - no car is ok, and can actually be easier, as parking around town can be hard and expensive. A kitchen in your accom would be good. Whilst the quality was always good I did find eating out in Queenstown more expensive than Melbourne. Wanaka - you will want a car.
There are shuttles from Wanaka to Cardrona and Treble Cone, and transfers to and from Queenstown Airport, so yo can do Wanaka without a car (I have several times, years ago) but you'd need to be staying within walking distance of the town centre if you want a variety of places to eat at night, or don't mind eating in at the right sort of accomodation. A link I found, no recommendations made: http://alpineconnexions.co.nz/Connexions/
Reckon so for original poster, well for me and OG1 as well being pretty much same category. Seeing as NZ works as a vacation with skiing rather than as a skiing vacation a car works very and if conditions mean the bus is a good idea no problem. And if not staying on the bus to Remarks then the car park at the base entry is an option.
Don't know if anyone read the OP's first question. 5 people (2 adults, 3 kids). The cost of a shuttle to ski is more than hiring a car per day. Hire a cheap car and drive.......you won't regret the freedom with kids, to be able to hit up the best supermarkets (cut costs) and go / leave hills when you want.
When we first went to Ruapehu, we happened to stop into a local ski shop there in turangi (snowscene.co.nz), and they were super helpful! Told us 1. hire off mountain (good idea too cos on mountain prices are crazy) 2. get up early as to avoid queues 3. pack lunch as again on mtn lunch is very expensive. I recommend talking to the locals as they know what there talking about and helped us (newbies) out