This isn't complicated, if you off-road your GS, you need protection. If you're not falling, you're not having fun. This is why crash bars are hugely important, but that's not the end of the story. On a boxer GS, your engine is sticking out waiting to hit something. The engine itself is actually super strong, but the cylinder head covers can be a weak point. It's another point of protection you should really consider.
Without extra protection, the head covers can display all of your hard earned battle wounds. Beyond that, the head cover itself can crack letting all your valuable oil out. Unless you can temporarily JB Weld it, just to get you back to pavement, you’re not going anywhere.
There are many options out there for this specific type of head protection, most of them thin metal coverings that do a decent job. Nothing I saw really made sense to me until I found the Machine Art Moto X-Head (LC). They looked great, cover a larger portion of the head, and to me, seem more protective than the thin metal offerings out there.
From the website description: "With its blend of high impact strength, temperature and UV stabilization, the injection molded shell is designed to be slightly ductile in impact to prevent breakage. On the inside of the shell is a thermoplastic rubber liner that rests against the face of the cylinder to aid in dissipating impact force while preventing hard contact" (emphasis mine).
I really drop my bike a lot off-road, it's part of the learning experience. I feel these add a layer of protection that I really need. Like I said, crash bars are not the end all engine protection when it comes to boxers. I've had them for over a year, this is a product I would buy over and over if I had to do it again.