"but if the club does not have good resident singers,"
If a club does not hve a team of competent ("good" is too loaded a term) turning it into a venue for guests is not a viable alternative - you may as well abandon running a club and just hold concerts, it ceases to be a club.
I suggest (or I hope) that your description of "half a dozen or ten regulars shuffling papers" or being "unprepared" - in which case an army of paid guests isn't going to make a happorth of difference
Unless club organisers get up off their collective bums and change that situation, they may as well just run concerts - I'm sure local councils would be happy to co-operate in such enterprises.
Personally, I'd rather there was a good local scene up and running before you embark on paying out for guests.
Jim Carroll