Ray, it may be the case in your area, ok, then make that clear, you cannot possibly know the situation on a national level unless you have visited every club or done a survey.
Jim,I think good resident singers, good guests and helpful volunteers are all essentials for a good club.
listening to dead singers can be helpful for performers to raise their game, so can being present and listening to Quality guests live.
Jim, how often a guest is booked be it once a month, twice a month three times a month does not prevent a folk club from being a folk club, very rarely in my considerable experience do Folk clubs book guest 52 weeks a year.
There are other factors, other than how frequently a guest is booked the define a "CLUB" from a concert. Sometimes this could be social interaction, extra club activities[ one example I have experienced has been Folk Club music Canal boat holidays, or folk club walking holidays, where the Club organiser has asked the club regulars and booked a Cottage for a few days, people have got to know each other better and maybe had some singarounds in pub whilst they were all on holiday.