Now there's an idea, just put all the names into a hat after an advertised deadline (and with plenty of time for the unlucky ones to make alternative arrangements ) and leave fate to choose the mixture of attending.There's a lot of for and against here, but I'm not seeing much in the way of compromise suggestions. For Golf tournaments they use a set system for potential players and I would have thought it might be adaptable for FUN meets.
Something like Group 1 - offer to all last years attendees; Group 2 have a points system for those who usually come but couldn't last year up to half of what's left, Newbies - in a draw or first replies for what's left (minimum 50% after Group 1).
Specialist meets could include a ranking for Ukes, canoeing, wine tasting or whatever.
There would be a reserve list of the next 15 drawn, of course!
You can't get much fairer than that!