Here in the Silicon Valley area, the social dance venues all tend to have more men than women.
Attendance rates here don't usually fluctuate wildly from week to week, but they do vary by time of year -- for example, I always notice the floor is less crowded when the fall TV season starts!
The music mix in this area has shifted slightly toward club dances (hustle, salsa, west coast swing) but only slightly; most of the places I go still have a pretty even mix of dances.
Age group varies dramatically by venue around here. One place I go for west coast swing (they also do the occasional waltz or foxtrot, but mostly WCS) has an average age of 55-60. At another place I frequent, the average is under 30.
One thing I've noticed, no doubt a peculiarity of the demographics of my area, is that the racial makeup of the crowd varies by sex. At several of the dances I attend regularly, the men tend to be predominantly white and the women mostly Asian. The difference is greater now than when I started a few years ago. I've talked to others who've noticed the same thing, but nobody is quite sure what's behind the shift.