The vendor said I needed to prime and paint them. If I like the bare colour of them as they are now, I'm hoping I can just keep it as-is. Is there a reason that I would need to prime and paint them? Will the elements, or something else, damage them if I dont?
Ultraviolet light will degrade them (specifically the plastic that binds the fiberglass together into the "fiberglass reinforced plastic composite material" that we usually refer to as simply fiberglass) if you do not prime and paint, and then they will start shedding glass fiber (which does not degrade, but does make AWFUL splinters), which is a horrid mess to deal with. If you like the color as is, and it's a color, try to match that at the paint store - otherwise (if it's a "fiberglass look" you are trying to preserve) consider a clear UV protective finish such as spar varnish (which will need renewing over time, generally more frequently than paint.)