That's just not how "performance" works. Stiffer =/= faster or better, ESPECIALLY in an Autocross where the pavement is likely to be rougher and de facto less grippy than a racetrack. For example, H-Stock Mazda3's in our area run faster times when they "upgrade" to Mazda5 oem shocks which are softer and have more suspension travel, simply because they absorbs bumpy pavement and keep the tire in contact with the ground much better. This is especially crucial for our cars and their open-diff one tire fires that occur even at partial throttle in 2nd gear.
That may be true in your area, but I garantee you nobody at nationals is running anything close to OEM anything shocks...if they don't do it there must be something to this stiffer = faster. I'm also listing this as a package deal. I'm not picking out just the shocks. I'm also talking about mods outside of SCCA Stock rules...more Street Touring. Where undoubtedly, stiffer is faster...obviously like everything else in life...to a point. Our club (which once again is the context in which this list comes from) doesn't use SCCA rules anyway, we use the NASA-X points based system. I have $5k worth of mods on my car and I'm still in the same class as when it was bone stock.
Long story short, your suspension should only be as stiff as you have tire grip for, otherwise it's just a waste of money. Also, adjustability is rarely a good thing for the Average Joe, as most people don't even begin to understand how to tune suspensions for optimum grip, they just say "crank the shocks to max stiff, must be better." The best mods for any sort of racing: tires, and driver mod.
Agree with matching suspension with grip. Absolutely agree with the best mods being tires and driver. These were clearly expressed in the club's thread that this list was pulled from. I agree as well with your adjustability assessment to a degree. Yes, Average Joe is going to do exactly/or exactly opposite of what you described. Or Average Joe could show some intuative and ask questions and learn and experiment if he is truely interested in going faster.
I am one who supports not driving daily in full autocross trim. When I go racing I adjust sway bar stiffness, rear ride height, compression and damping settings, front toe, as well as putting on my sticky street tires. I'll add camber to that list when I get plates. Adjustability in my mind isn't just for tuning, it's for livability on the street too. Lastly, a great autocross setup on a 3 is not terribly rewarding on a mountain road. It's nice to be able to somewhat neutralize the car.
My experience in my 3 is stiff + low + adjustable + sticky street tires = multiple seconds faster than stock no matter what the surface condition is.