That's mostly due to the Shelby GT's having been lowered 1.5" from the OEM springs.... It is easier and cheaper to just "tweak" the range around the spec than to put money into the cars to give them adjustment to set them back to around -.8.

 

Flash forward...15k miles later and my tires are nearly bald on the inside tread

Any suggestions for a reasonable negative camber? I'm thinking of having them set it at -1 degree after I buy camber bolts from Strano.

 

Assuming you can trust the racks and the toe wasn't all jacked up (I'd just run zero for minimum scrub), you just don't drive the car hard enough in corners to need or want much negative camber, and should set it back to a more stock like setting.

 

In order of expense, high to low:
Camber plates, or
Camber bolts, or
Undo the four strut mount bolts, drop the strut down and turn the mount the exact opposite of what it is now, then bolt it up again. You can gain up to .75 positive camber that way.