I think the biggest impact is on the industries or businesses that rely on the racing industry & events. For example the transport, vets, feed merchants, accommodation, catering, horse breeders, trainers, jockeys, agistment, betting, tourism, etc, etc.
Any affect on a major industry will affect other subsidiary companies that rely on the major industry to generate trade. Same issue with Car manufacturing industry.
I have always thought that the biggest threat to Oz is disease. A major disease outbreak (eg foot & mouth) will have a greater and longer term impact. This would impact people & the Oz economy more than fire, flood or other natural disaster.