I'm generalising here so do not take it personally, The people wanting old bikes is diminished, they generally tend to be older people,, (stating the obvious) .... These people probably ride less than 2000 miles per year and they want a bike that starts after 4 months of neglect.. Therefore old bikes are not the answer. Have an old bike if you can spanner and fettle a bit otherwise they are left alone.. I bought a 1983 XS1100 for £300 with a blown piston. I had it stripped to the frame and powder coated. I rebuilt what I could and had a mate rebuild the rest. At that point it was about 90% original.. But it didn't like being left in the shed.. I'd ignore it for a couple of months it would take half a day to get it running , so I upgraded the electrics had major work done on the carbs and the bike stood me at £2500, Ebay value for unsold bikes £3500. Tried to sell it a few times ,, no takers. auction !! bids nowhere near. finally sold the exhaust for £500 and the Cowl and screen for £300 and the bike went to be chopped for £1250.. IMHO a lot of old bikes are worth less than you would think ,, with a few exceptions