Good fun eh?
Ultimately it's what you bank yourself that counts - a fair point lower down the thread I thought, it's more about the individual trader... I know of different people using the same basic 'system' yet some are winning, others losing, which has pretty well convinced me you can with with anything sensible... it's what's inside the trader that determines the end result to a large extent.
It seems to me that it is probably also possible to teach others well, but be bad at it yourself - you might impart pearls of wisdom but be too underconfident to stick to it, whilst gullible customers fall for it, stick to your method, and make a nice profit. Maybe that's what was happening?
Even the worst estimate was that he left just over £100,000. In 1955 that wasn't a bad sum of money. It would probably be a few million today.
I am sceptical about a lot of the claims about Gann but some of his methods do seem to work well. 'Marc Rivalland on Swing Trading' was one of the best selling trading books last year and he uses a modified Gann swing chart.