And that is the reason I dont want to restore them myself, I rather buy one in stock trim, or one that has been restored already 
As long as you are knowledgeable to recognise a well-restored bike from a coffin.
I have seen restored bikes that needs full rebuilds, yet are very shiny.
Any model is at it's most valuable in stock, unrestored trim, given it is spotless of course. Any bike is only original once, after a rebuilt, it can be re-rebuilt many times.
For many the true joy lies in doing the rebuilt themselves.
But if one properly, it can nevr be a money-making business. Not anymore, anyway, with classic price now.
I spent years judging the concours at the Toy Run and Beaver rally and I used to be amazed at the bikes , there are the guys that do a full bolt and nut rebuild , but there is no petrol or oil in the engine , sorry but no running no points , the other lot are those that bolt on a whole bunch of accessories and think they have a winner , there are the guys that do an amazing rebuild but fuck it up with ND bolts , gutter bolts , rusted bolts and the worst for me is the rusty rear brake spring .
Then the one that scored highly with me , the original unrestored , well used and neat bike , there was a Z650 at the Toy run that won for a few years , original apart from a set of stainless silencers , the bike was in daily use and had high mileage but was very neat , in my eyes a winner .
Needless to say there were lots of pissed off people , especially at the Toy run , the one year a concours competitor complained to the organisers , so the late Keith Bright was brought in to do a second judging , same result solved the problem .