FYI: Unfortunately, tires will probably be your biggest expense autocrossing. And, as you know, Corvette tires aren't cheap! But that being said, you'll be able to use your tires a heck of a lot more than 3 or 4 events.
As Rick said, the junk on your tires is OPR and nothing to be concerned about. Your driving style will have a significant impact on longevity. You were riding with a lot of fast people, so you were driving pretty aggressive by the end of the day (
). Of course, that newly found aggression meant you were sometimes a bit too hot into some of the turns and plowing a bit (understeer) which is pretty hard on your front tires (i.e. they're turned sideways while the car is pushing forward just grinding at them). As you get your aggression dialed back appropriately, that radical wear will go away (and you'll be faster too!).
I drove on 2 separate set of PSS's when I first started. As we discussed, PSS's are sensitive to too much heat....if you let them get too hot, you'll have chunks falling out of the outer shoulders. My first set I didn't water at all (and I was the king of overcooking every corner and understeering like a fool). After one hot summer practice, I looked at my tires...and they were missing big 1/2 inch chunks in the shoulders....still plenty of tread...but chunks missing and exposed cords. So after getting the "get a tire sprayer" advice, I put on another set. Religiously keeping them cool did really help extend the second set (and of course having Tom Berry rolling his eyes and shaking his head after every lap that I over cooked everything may have helped a bit too!). Those PSS's lasted much longer than the first set (better driving on my part and better heat management as well). But....after 2 sets, I decided that the PSS's didn't have the "shoulders" for the excessive edge wear of autocross and started looking at other tires.
That being said, I wouldn't recommend buying tires any time soon. You've got a decent set of tires to start with, and working on your driving skills will yield far better return than throwing money at tires at this point. As I remember, my PSS's lasted over a year of autocrossing and daily driving (and I was autocrossing more than just SCCA events) each set. You're going to wear those tires for sure, but assuming you jumped in with both feet and start attending every event and practice I'd be surprised if you don't get at least a season or more out of them.
Real World Numbers: You drove my car with Rival-S all the way around (Rival S are one of the competitive street tires available in Vette sizes). The Rival-S is a softer tire than the PSS and you wouldn't expect them to last anywhere near as long as PSS. Those tires have about 220 laps on the rears and about 180 laps on the fronts (and maybe 6-7K daily driving miles). They are close to done (at least for competition)...but I'll probably use them at least a few more practice days. I tend to drive my tires till they are completely toast just to keep my budget down where I can. The tires were competitive till about 140 laps....and then slowly have fallen off a bit. That being said, I had some great results with those same tires this last weekend, so no need to scrap them quite yet!
Anyway, our tire gurus may chime in here with some additional thoughts for ya!