If you are without car and not really in for camping I would suggest renting an RV. It's the happy medium - you get from point A to point B, don't have to camp, have protection from the elements and as a bonus if you are adding days at the front or back of your trip you can park overnight for free in Walmart parking lots all over America which saves you on Hotel $.
Friday camping won't be a problem, just be prepared to pay for an extra night. The campground is huge so you shouldn't have a problem finding a sapce if you come on Sunday but it will likely fall under the less desirable placment further from the show area
eleanorh - If you do fly I would recomend having a look at flights from Buffalo. My friends and I booked return flights with only one short stopover each way for $240 return taxes in to Portland (Seattle was about the same but we wanted to see a different city this year. Between 1/2 and 2/3 of the price of Toronto to Vancouver
Doubtful that you will be able to show up just after midnight to escape the extra fee. I guess it depends on how charming you can be. If you are looking to get up close you really don't need to worry about getting in that early. The first spots to fill up are on the rockface which are actually quite a ways back and there are many that won't even enter the grounds until much later in the day.
Do you think the Ryan Adams opening for Oasis in Seattle at the end of summer eliminates the possibilty of him being added? It seems far enough off that it wouldn't, but it could explain why he appeared on the original poster and is now gone.