Well, I went back to the figures and checked masters divisions figures.
The top 3 Masters division for Men were as follows for 1991-2001.
1992--Pittsburgh---220 male competitors
1995--Indianapolis--210 male competitors
1998--Villa Park--215 male competitors
Results were consistent with Sr. Male competition and Masters divisions wouldn't be affected by competitors wanting to get roster points.
Masters divisions for California were
1990--San Diego 204 competitors
1994--Irvine 173 competitors
1996--San Jose 166 competitors
Personally, I'm with USAJUDODAVE. If I'm gonna go watch the nationals, I want it to be in a place I can get to cheaply on a direct flight and I want the weather to be nice. I don't own a real coat anymore, and don't want to ever have to wear one again. I've gone to the California and Florida events; and would have gone to Vegas but I had other commitments.
Seems like common sense to me, but when I checked the figures, it proved to be a false assumption on my part. Whether its a major market or not, doesn't seem to have any bearing on number of competitors.
As for spectators, I dunno. Pretty much the stands are filled with people who are involved in judo, or involved with people in judo. I don't think that changes much at any of the nationals.
Here might be a better explanation.
It is a map I found of USJA clubs on their webpage. You can see it here.
When you consider that JF is pretty strong on the east coast as well, might give a better reason for the turnout. If this assumption is correct, Virginia Beach could very well put up some impressive numbers for competitors.