I started an alternate Thursdays folk club a year and a half ago and it has been very successful. I did debate the pros and cons with myself before deciding. People seem to be able to able to manage their diaries well enough but I did collect everyone's email address and I always email a reminder the Monday before. Plus I do hand out postcards with the meeting dates for the year which they can keep in their wallet or pin up at home. Plus I do stick up an A4 poster in the meeting room (right beside the bar) with the next two or three meeting dates in bold red letters.

I thought every week would become a little bit automatic and boring and that having to wait a fortnight would create just a little feeling of "can't wait" which could be positive.

I truly believe that it doesn't matter much whether it is weekly or monthly. For a successsful club, there are more important things to get right like creating a really friendly place, welcoming and inclusive. And to work hard to get the "atmosphere" - now that's just about indefinable but you know it when you encounter it.

We have our eye on the alternate Thursdays we are currently not using We plan to run different events on those. One maybe to be an instrumental session evening (with a few songs) and another to be a "floor spots" evening to provide our many better performers the chance to warm up in a 30 minute slot. We haven't done this yet but are building up to it.
Cheers
Roger