Matty, I am a PIARC member and have done 4 or 5 events now at PI. Not bad but not as sharply run as WRX/SUA event. I went to Winton in July (my first WRX.SAU event) and got to say it was very well run (except for trophy pres at the driver's briefing WTF???).
As per previous comments, PIARC groupings can be a bit ordinary. Example - I was blasting past my mate in an Elfin (me 220, him 190), focussed on giving him plenty of room on man straight when some hero in an ex V8 Supercar blasted past me at 250+ three abreast, one wheel almost off the track. Massive difference in lap times is dangerous, didn't see him coming.
Having said that, I keep going back for Saturdays because you get a heap of 15 - 20 min sessions, rooted by the end of the day. I have my own GPS lap timer so lack of timed sprints is no drawback and I prefer the less serious attitude and extra track time. Quite a few leave early on Sat so late in the day, sometimes you get open pit lane, go out as much as you like. Awesome.
Last time there my brother and I shared the car and did 60+ laps in the day. Not good for the wallet but great fun.
Cheers.