There is plenty of space, but that depends on how early you arrive. I'm not sure when Illium camping officially opens for festivarians but I do know that by Wednesday evening things start to get much tighter. Eventually everyone will be on top of everyone else, but if you are able to get there Tuesday or as early as possible on Wednesday you will have a much better chance of finding your "perfect" spot.
Also, if you can find a space that has trees to East (towards the road) of you, you will wake up in the shade as the sun rises, rather than in an oven getting baked by the sun.
Dave