Thanks, I hadn't considered that, and it's a good point.
Although perhaps I'm an oddity: I rarely see myself as among the speakers so I don't look at them as a guide. Also, I've been to "gender-equal" conferences where almost the only women there were speakers. So speakers != audience
Speakers != audience all the time - the audience won't be an exact match for the speaker demographics. But having done this for a bit, I've had enough feedback that indicates that having a more balanced/diverse set of speakers is a signal to a wider audience that there will more likely be a wider range of attendees to socialize and network with. Again, yes, not 100% all the time.
FWIW, at indieconf we had about 30% of the speakers were female. About half of the attendees were female as well. Interestingly 30% answered the 'gender' question as female - 30% answered 'male', 30% left blank - I'm assuming based on names given about half of the remaning were also female - that's where I'm getting the ~50% were female.
Although perhaps I'm an oddity: I rarely see myself as among the speakers so I don't look at them as a guide. Also, I've been to "gender-equal" conferences where almost the only women there were speakers. So speakers != audience