Nathan

I would definitely avoid the early part of the week (23rd - 27th) when
the field is very full. Later in the week - Friday 29 - Sunday 31 -
would be a good time to come. The field tends to start thinning out
later in the week and you wouldn't have trouble finding a spot.

The last day (31st) might be a good call. You get to see a historic
moment - last flight of SpaceShipOne/ White Knight on their way to the
Smithsonian. Also, there are always some GREAT last day discounts on
offer in the exhibit hangars. I always make big purchases on the last
day and have saves $100s on GPS and parachutes.