Historically, summer meeting attendance tends to be lower.
Back when I was pres, we generally met monthly on I believe it was the second Friday evening of each month at the Union Hotel restaurant, except for when members offered to host. In my opinion, the switch to every other month weekend meetings hosted by members appeared to increase attendance.
Working in SF, I prefer weekend meetings, as then I don't have to endure the commute out of the city only to have to drive north to Santa Rosa.
I agree with James that a consistent date such as he suggests makes planning easier.
Again in my opinion, our lack of an active social media presence on any site is a significant factor in our less than robust attendance and we are missing an opportunity to attract new members.