My wife and I spent 5 days prior to a company trip in Sydney, and had a blast. Dramatically different than Cali wine country, as the Barossa is much more rural and farmlike; McClaren Vale, which was a day trip for us with the night in Adelaide, was more developed.
We made appts in advance with several folks who were EXTREMELY ACCOMODATING and helpful; Matt Wenk @ Two Hands took out all the stops and opened more than a dozen wines for our 9am visit; even the tasting room staff was blown away with some of their high-end wines that he had opened the night prior. We had tried connecting with Ben Glaetzer (Amon Ra, Mitolo, etc) as we'd met with him locally for dinners in the past, and while he was out of the country at the time, he had several barrel samples and bottles waiting for us in our cottage when we arrived. His assitants also contacted me several times in advance offering advice, recommendations, etc. Our Barossa visits also included Penfolds (okay), Kaesler (excellent), Grant Burge (++), Yalumba (-), Lehman (-), Jacobs Creek (surprisingly excellent), Trevor Jones (eh), Torbreck (very good) and several others I'm not recalling at the moment.
Our lodgings in Barossa might be too "romantic" for a solo business traveller, but we found the Stonewell Cottages (see reviews on tripadvisor) well-situated and reasonably-priced on a lake in the middle of vineyards. Spectacular. We also spent a pleasant night in the Treetops BnB (also on tripadvisor). One of our best dinners (ever) was at Appellation, in the high-end micro-resort called Peppers, The Louise. If I was travelling with business partners on expense acct, that's where I'd stay.
Our day-trip to McClarenVale had two stand-out visits; first was with Justin McNamee, owner/winemaker of Samuel's Gorge. This is an up and coming property and Justin makes OUTSTANDING WINES. His tempranillo was my first, and has since become a house staple. Kay Brothers Amery was another winner, with Colin Kay breaking into countless barrells to sample various vintages of Block 6, which comes from vines planted in 1890, and other wines that aren't even for sale, just for family events. We also stopped into PennysHill and a few others, but I'd go back just to see Colin and Justin.
We found a great deal of hospitality just by contacting people in advance and letting them know of our interest in their wines back in America. The Aussies really do like Americans (or they're great fakers) and we found ourselves given parting bottles of wine gratis just for coming by. We also made a point of offering to share some great US wines with folks during our visits, and as a result found big names in the business willing to join strangers for dinner, and send us off (half-cocked) with lots of their own wines as thank-yous. Thanks for reminding me of the great memories just by typing this out!! Enjoy and feel free to contact me with questions.