As the boys said Tony, the value has to represent the current replacement cost. If you think about the fact the supply of panels is drying up and NOS panels are going through the roof in terms of price, not to mention the price of all parts in general has rocketed in the last 12-15 months, if you have a genuinely rust free Beetle then it's worth a lot of money nowadays.
I was lucky to get the last n/s door from VW Spares for the Cal Look. There are none available in the UK apart from used items. You will not get a Beetle restored for less than €12k these days, not including the cost of buying the Beetle in the first place so don't be afraid to value your Beetle at a price that reflects this as you have done a full body off resto on your car as well as loads of upkeep. Ask Riggsi, Jon White and Emilio if you're in any doubt.
Both myself and Trev are gathering parts for our next restorations. Trev's restoring a '73 1300S and I'm restoring a '72 Anniverasry Beetle. We can both tell you how hard it is to find good panels and if we're lucky enough to find some we're paying a lot more than we've ever paid for panels. They just don't exist anymore so by the time we're both finished we'll be many thousands of Euros into each Beetle so if someone was to buy them they'd have to step up and pay the real current (rising) value. The same applies for your Beetle so value it accordingly.