Well this didn't go over too well in the other catagory,
Taint? Really? 
Rear Axle Skid Plates. Are they worth the @ $200+? Do they really work?
No they're not worth $200. Yes they will protect the bolts.
Is there anything better than the "blue painters tape" to protect her from getting brush scars? That 3M stuff?
Frost King clear tape. But real wheelers wear their scars with pride. 
Last one (thanks for the time): has anyone damaged their rear diff? Should I get the Rear Differential Skid Plate also?
Yes. No. You're not likely to damage the pumpkin hitting it in the front, unless you try really, really hard. The Purple Cranium protector will protect the diff cover, which is most vulnerable, as is much cheaper.