Which would you upgrade first tires or suspension?
The car in question is my 98' Camaro with 105k on the clock, so the shocks are showing their age but still function. Same could be said of the tires, I have a decent set of 16's with good tread for the summer, and a dedicated set for the winter.
The car is a daily driver year round that I take out for fun every few weekends. Mostly exploring back roads with two or three autocrosses throughout the year. I'm not a hardcore competitor just out to have fun.
If I went for tires I would probably want larger 17-inch wheels as well to maximize the width, currently I max out at 245 tread width and still break them loose fairly easily.
If I go for suspension it would be the recommended autocross setup for F-bodies from Strano, SLP bilstein shocks and mild lowering springs.
tyres are the easiest.. but too much grip is no good if the car is moving around on it's suspension too much.
I would go suspension first
If you need tires go there first. If your tires are new and there's not pressing event you need to attend, then work on suspension.
There's no magic order since usually it's done a piece at a time instead of all at once. Know your goal and where you are headed so that everything works towards your goal. In other words don't wimp out in the middle and install a non matching part cause it's available at a good price.
I've bought less than stupendous tires while I work on the suspension because I knew those tires would need replacing about the time I've finished working on the suspension.
Fix the broken E36 M3 first. Your shocks were done many, many, MANY miles ago.
It's just like you can have 1200hp stuffed into a 400hp capable chassis..... You are still going to get your ass beat in to a 120hp FWD Honda.
Suspension doesn't sound like a bad idea, it did tend to lean a bit last time I had it out 
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Powaaaaaar!!!!!!! Tires and suspension just keep your car from dragging on the ground.
I'd say suspension first, but if your camaro goes anything like the way the string of mods to my Miata went, uprating the suspension is just gonna work the poor abused tires harder (I'm remembering how much easier it was to overwork them/make them slide after fitting the FM swaybars compared to before, since the stiffer sways made the tires take up a lot of compliance that was reserved for the suspension before)
Start with a good set of shocks, maybe stiffer sway bars. Seeing as this a DD, I'd tread carefully before getting too stiff on springs and bushings.
Sounds like you have good tires and probably worn out shocks. I'd replace the shocks first.
Tires. You'd be amazed at the car control you can learn with good traction but a busted suspension.
I'd say shocks first. The DeCarbons your car came with are shot by now. Next on my list would be front sway bar. These will keep you in stock class at least. Tires would be third ONLY because you said you already have two sets and you only do two autocrosses a year.
Oh, and check the front lower control arm bushings while you're in there. They tend to go bad on these cars.
I look at Tyres as being like shoes. You can have the best running shoes in the world, but if the legs are not in shape, you are not going to do well in the dash
Tires are part of the suspension. If you buy new rubber and have bad dampers, play in the bushings or fixtures... (ball joints/tie rods/etc) all you did was increase the load the tires can place on the rest and accelerated the wear of both.
On an old, high mileage car, bringing the suspension back to new or better would probably be the best thing to do.
That includes all suspension bushings as well.
