As it is a Targa, the roof will influence value in Australia. But why ask us as none of us are involved in the car trade more broadly? If it was me considering such a purchase I would call one of my friends in the classic car sales business and discuss the car's value and future merits.
As others have said, the Australian market is different from, e.g., the UK market. There, Targas and Cabs are valued higher than coupes, but the reverse here. It's probably a weather thing. Mileage is a factor but the service history (inc IMS) is more important. 997.1 is less than 997.2 generally. Add the difficulty of getting Targa parts, then a lower value than a commensurate 997.1 coupe.
Car Sales prices really are no guide at present and there are some bargains out there now, if you ignore some of the prices being asked and make your best offer and be prepared to walk away. If you know dealer or trader - phone them and discuss it! My 'guess' is based on what I would pay and that would be between $60 and $68K, if everything about its condition, PPI and history stacked up, and I 'really' wanted a Targa. But that's just me.