My initial thoughts was surely you want the cheapest official valuation so you pay less tax (10%?) and avoid luxury tax (another 33%?).
However from a quick Google.
This involves obtaining an ‘Australian landed valuation’, as imported, and as valued by an independent Australian motor specialist less a series of deductions and the figure remaining is deemed to be the ‘customs value’ upon which duty and GST is levied. The importer is responsible for obtaining, as well as the cost of the ‘landed’ valuation.
A valuer may at first consider the market value of a similar vehicle in Australia and make a significant reduction for the fact that the vehicle has not yet been imported and registered. From this figure can also be deducted all the subsequent costs of getting a vehicle ‘on the road’ and then deducting the 10% GST and then the 5% duty (and where applicable on very high value cars the 33% LCT). From the remaining figure customs would then deduct all the costs of shipping the car to Australia to arrive at the ‘customs value’. The resulting ‘customs value’ can be as low as 50% of the actual ‘Australian full market value’ and in most instances is a system that benefits the car owner / importer.
So you want the cheapest official printed valuation from a registered car dealer I guess. A Jaguar dealer would be a good place as they will no doubt price it low in the hope of buying it and it should be on some official Jaguar bit of paper. Hope that helps. I've learnt something new.