i don't know how they work the races, but i went to a free practice session for irl at fontana and it was awesome. you could go everywhere...literally, i could have driven my car onto the racetrack, but i'm sure that wouldn't have been a good idea. the fans that showed up were being very respectful of the drivers and crews during the testing, i'm sure partially because all the drivers were going to sign autographs after the practice was over...but several people went right up and talked to some of the crew members when their car was on the track.
it was really total access...one thing that surprised the heck out of me is that i was able to go right onto the pit wall, lean over it, and take pictures of the cars as they were coming towards their pits, without any security giving me a second look...as i said, i could have done anything, drive onto the track, run across it, smash millions of dollars worth of testing equipment (geez, i sure do have a destructive side, glad it doesn't control my body, lol) and nobody would have been able to stop me until after i had done the deed.
oh...the point is...it was awesome to have that much access, even if it was only testing.
I got a pit pass for PPIR a few years ago during the Busch weekend, it was ok , not really worth the money. I think during practice and qualifying it was the best because my buddy and I could walk around the infield area and watch the cars entering the turns from a totally different perspective. The garage pass is the one you really want, very hard to get unless you are involved with Nascar either indirectly or directly. By that i mean connected to a sponsor, working for a company that has connections , that sort of thing. I don't think you can buy garage passes, but i could be wrong on that, i know different rules apply for different tracks.