Height should be a factor too.
goth dudes tend to be the tallest for some reason?
Height is not, in a practical sense, a finite resource unless someone comes in who is 40' tall or however high the roof is. Square footage DOES get filled and it gets filled quicker when hambeasts come to concerts.
fat people take up square footage, reducing how much is available to you, and thus reduce your enjoyment of the show.
tall people take up vertical space, reducing your view of the stage, and thus reduce your enjoyment of the show.
if we start charging extra to one group, we need to start charging the other too.
while we're at it, let's charge all groups that might potentially limit our enjoyment of a show: sing-alongers, dancers, anyone with bad breath, people who make fashion decisions we disagree with, etc. etc. etc. surcharges for the lot of ya!