Personally, I think Leica has done the collector's market to death with its commemorative models ("50 Minutes Since We Last Thought Of Something To Commemorate", etc.). As far as I am aware, no one has gotten rich by buying these, I think almost all can be bought today for less than the original price. I think Leicas will continue to hold their value relatively i.e. better than other film-camera brands but will not be unaffected by the extreme contraction of this market.
PS: Your post is headed Leica III cameras. If you can buy some of these new at 1933 prices, it would certainly be a great investment !