I've been to a few swingers clubs, and find that there are a huge range of ages, body types and people that attend, from 20 somethings to seventy somethings, (I'm nearly 60) and from gym fit to dad / mum bods, BBW's and everything in-between.
As @GentlemanJay has said, the social side is just as important as the sexual, if not more - if you don't make a connection, then it's not going to happen.
The downside of swingers clubs is that you can (and sometimes do) get single guys "pestering" women / couples, (walking around in towels or less, often with their, er, appendage in their hand...) particularly after the pubs get out..
Not been to a KK party (expensive, and imho, elitist, and yes, I'm a KK member), so can't comment, but KK is female led, and guys can't attend most of them unless they have been invited, so less issue with the "wanking dead".
I'm looking forward to returning to the clubs come next week!