Hi Mike,
As far as damage to your motor, it's probably very low risk since you've shut the motor off each time it's looked like you were about to overheat. It could be a small leak, and that's why you're not seeing a lot of smoke. I've never replaced the head gasket on a crossfire, but I've replaced the head gaskets on 4 different chevy 3.4l V6 engines, and all of them have gone into the red, or had clear overheating signs (water gushing out of the coolant reservoir) before I replaced the head gasket. After the head gasket replacement, (and valve job since I had the heads off) at least two of them lasted another 100k miles, and the other two are still on the road. One of them I had a hard time diagnosing since the previous owner had used a boat load of head sealant before he sold it to me - eventually (couple of months) that wore out, and the car started to overhead randomly. Ended up replacing water pump and radiator before just biting the bullet and replacing the head gaskets. I don't think the crossfire head gaskets will be that hard to replace since you have access to everything.
Good Luck,
sincerely
Jerry