Last April I had an opportunity to explore the Hunter Valley. From Sydney this required an early morning train for about two hours; if there are more then three people it may be worth while to just rent a car (providing you have a designated driver). I recommend the train+tour approach which includes a designated driver.
In the case of http://www.textours.com.au/ the driver is literally named Tex. Tex fulfills your quotient for Australian language (something you may otherwise miss out on if you stay just in Sydney).
Tex picked us up from the train station in his little white bus/van and drove us around all day. We hit about five wineries, plus a cheese & gelato stop and strange fruity things such as quince paste (for cheese & crackers).
I believe the cost was around $60 per person plus train tickets, but it was worth it. Tex was hilarious, informative, and very accommodating.