I've seen it a fair bit lately too, there were a couple of hd8's for sale on gumtree, the bloke wanted $1000 each and they weren't complete nor running! Not sure what people think they have when it comes to this stuff, my other HD was advertised for $500 but i told the lady that it was only worth about $120 and she did eventually take it... the other side of the situation I've seen is I have a fairly new power torque here in good running condition, advertised it a month ago for $100 and not even a bite!
Ultimately the vintage stuff is only worth what someone is willing to pay, the most I've spent is $500 on a pair of ranchers, mostly complete both running with extra parts!