The safety can be worth it in certain cases. Like when handling untrusted input. And it's not just Rust: look at WUFFS for example. WUFFS can actually rival handwritten implementations in certain cases.
Forgive the ignorance, I have worked entirely in the abstracted layers of the stack, and mostly web.
Whether that counts is up to you. I suppose it's still "sandboxed" in that it runs in a less privileged context than the kernel.