I've attended a few star parties started the week ahead of Labor Day and ended on the day before Labor Day (the Sunday). I actually like that schedule a lot, because it has me traveling home on the Sunday in the middle of a 3 day weekend.
Just about any star party I go to is outside of the Seattle area. There are limited routes in and out, so on any given Sunday afternoon and evening, it's not uncommon to encounter multiple hour traffic delays, no matter which route you try and use to get home. The exception to this is a Sunday afternoon in the middle of a 3 day weekend.
I'm in a big minority in this, though. Oregon Star Party is the one that could potentially bump into Labor Day. And when they end on that weekend, they get lowered attendance because families with school aged children tend to stay home. Since I don't have any school aged kids, what works well for me, doesn't necessarily work for the majority.