Having only visited Calis in the busiest part of season (July-August) when a lot of families are out, I've found B52 is always busy then and usually around 11:30 to 2am it's at the peak. Mostly with people around my age who have escaped the parents for their own time away! The style of music usually appeals to my generation too - not wanting to sound rude about that, but usually whatever I hear on Radio 1 I'll hear there in the summer. Essentially, they appeal to one demographic but I understand the opinion about a prime location not being used to full advantage.
Coming out mid July this year, so who knows if it'll be the same as the last time I was there in 2011. Either way a review will be posted!