Just my few thoughts if of worth... Hahndorf is barely 30 minutes from the city. Free, easier and more convenient parking in the nearby residential streets - unless you know of the 'secret' usually quiet carpark under some trees.... And always very good food at the German Arms and other such restaurants. Definitely a thing for visitors, with some nice nearby foodie shops (stock up on your Berenberg jars, folks) or nearby walks along the Heysen trail.

Of course, there's a Barossa road trip. Is that a given, by the sounds of things? Chateau Tununda or wherever.

Glenelg - does that Stamford hotel do a nice lunch, perhaps? Lots of other eateries around there too, and it's also very close to the airport.

Any river-side venue? Heck, y'all can hire a little paddle-boat after a DIY river-side picnic bought from the Adelaide Central Markets. Also, Adelaide oval stadium tours for those so inclined. Is there any sports match or theatre production on that weekend? Art Gallery? Museum? Botanical Gardens? Plenty of good classic pubs too.

For the organisers - can we get any private tours at ADL airport, like they've done at some DOs? No idea if we have contacts for such a thing, however.

Extension activities for those with deeper pockets or miles to churn: KGC or PLO or even MGB?