I totally agree on all points. I would not replace it.Yeah, it is pretty expensive and complicated for something that is invisible and not really essential for operation of the vehicle. 20+ years ago no cars had these and they functioned just fine! I think the main purpose / function is to improve undercarriage aerodynamics and thus fuel efficiency. I have no idea if it ads 0.1 mpg or 3 mpg
If it were mine, I'd be wondering what actually harm, if any would result in not replacing the cracked shield.