When I hit a load of gravel spilled on the road and had a low speed slide these are the areas that were damaged[You must be registered and logged in to see this image.]
The tappet cover was scuffed and the plastic broken. I built up 6mm of fibreglass to protect the vulnerable tappet cover edge then wrapped it and the plastic part in carbon fibre. For further protection I added a stainless steel rub rail.[You must be registered and logged in to see this image.]
I bolted on a series of stainless steel cap head set screws to protect the oil cooler shroud[You must be registered and logged in to see this image.]
The carbon carc protector that came with the bike was scuffed but not worn through I added a 4mm plate of carbon fibre and a stainless steel
sink blank.[You must be registered and logged in to see this image.]
I replaced the fixed brake pedal end with a folding one[You must be registered and logged in to see this image.]
I've not done anything to the handlebar end as scuffs on it would not prevent riding and can be repaired
In my opinion the most important part to protect is the tappet cover as once it wears through and the engine is contaminated you've got a major issue.
Next is the carc as replacement is really expensive.
The fixed ends on the brake and gearshift pedals are a problem from even a static fall as all the weight of the bike comes onto those ends, pretty much guaranteeing some thing will break. My replacement end bent saving that issue but meant I had to limp home with no back brake. It broke off when I tried to straighten it.
Protecting the oil cooler shroud was easy and replacement unnecessarily would piss me off
On the other side the headers and muffler would suffer most and can't really be protected. The gear shift pedal end I replaced with the folding option.