My observations are that there at two distinctly different groups of soul nite / nighter (grouped together for ease) attendees.
The main group prefer a predominately Oldies based set, often described as top 500 but is broader and includes many rare tunes (because some are) and of course littered with underplayed.
Attendees typically attend Hinckley, Nuneaton, Loughborough, Stoke, Skegness (Main Room), Torquay Main Room, Rugby Main Floor, Wellingborough Main Room, RSG etc
They are in my view the majority.
The second group prefer Rare and Underplayed and more progressive elements (in the variants, such as RnB, Funk, Latin etc) - funk coming to the fore at the moment.
They will frequent Lifelife, Bidds, Rugby Second Room, Groovesville, Gloucester Second Room, Southampton 2nd Room, United Sounds Of Soul, Move On, Bournemouth Railway Club, etc
They are in my view the minority.
Some like both and move between the two of course, trying different things, but most people I have met tend to sit 80:20 in one camp or the other.
I don't think either is right or wrong, its personal choice. Is it a split scence (think was original question) - can only talk in recent history terms, I'd say there are two main different strands under the same Northern / Rare Soul banner. It makes knowing the venue music policy and djs they have selected all the more important in my view.
That's my own opinion based on what I have experienced / seen for myself. I have attended all the example events mentioned over the last 5 years or so.............