The club I ride with (errr which is a far lot less than I like) is IMBA and spot on. Good bunch and a good laugh.
I noticed how much I learnt, my motivation, my fitness etc grew very rapidly when I joined the club.
However with life etc we all like different things and its not everyones cup of tea.
What I find that suits me about the club I ride with is, its simple. All were doing is riding a bike, thats it. We have rides on a certain day, its worked out the forum / phone and thats it. No mass meetings re rides, no fee when you ride etc. If the club needs a few quid for IMBA membership, we all slap some coin in where and when in the pub.
Simples.