my default answer is: the engineers at Yamaha put those on the fender because it was necessary. Of all the things that you dont want to happen on a motorcycle, the fender coming off the front wheel and getting thrown in front of it is near the top of the list.
You are right about finding used parts. Vstar bikes are incredibly reliable, you can expect the engine to last 100k miles without splitting the engine case open, but some people do manage to run them out of oil, or never adjust the valves and eat one... so there are bikes being parted out all the time.
Fenders get bent and mangled, check a website like bikebandit.com and you should be able to see what an OEM replacement will cost - that can be your worse case baseline if you shop around for used parts.