No one has heard everything, that includes Phil. The topic is about collecting isn't it, not DJing? Either way there are plenty of hidden, forgotten and ignored gems that won't break the bank. Throughout the history of the scene many records were out of the reach of the ordinary collector, price not always the issue but where you were on the pecking order with many of the top sounds never getting further than the top few DJ's at the time. Now at least most of the 45's that come to market everyone has a chance at if they have the money that is, they don't disappear to a select few.
Of course the large majority of traditional northern soul dancers have been found, what does one expect after the USA has been scoured for 40 odd years. But that isn't to say that things are still turning up now and then and that people are turning to the many 45's ignored when they once had a large pool of records to choose from. Tastes have developed and matured.
Plenty of venues thriving on these records so it isn't all doom and gloom. I will agree with Phil that the nighter scene is on life support. Too many offer nothing but what has been hammered to death already, formulaic DJing with no imagination, all following what the others are doing.
But as far as collecting goes, plenty to satisfy all bank balances IMO.