LONG POST WARNING
A lot of people made some good points in here already.
It comes down to a few factors.
Just to give you my qualifications. I have stock quarter panel S14s.
I'm a poor peasant who's only going to run 18x9 wheels on reasonable spec tires with an appropriate ride height.
None of my fenders are rolled.
I decided against fiberglass over fenders many years ago.
The only time I'll reconsider it is if some kit car manufacturer decides to manufacture S chassis
https://www.panchkits.com/
^ These dudes made an R34 kit car I believe.
I was even considering it for my Subaru as some guys was going to replicate the 22B widebody kit in metal but he hasn't gotten to it yet
and I'm already heavily invested in the wheels that I'm running on that car.
Are you keeping the car until you die or is resale in your future?
Modify if you truly are keeping it as long as possible or stock fenders (repair if rusty) since it will help resale value.
Cost
It is cheaper to fix a dented/rusted quarter panel than it is to get a fiberglass kit and get it properly installed. It's just a REAL pita to find a bodyshop that has a good work quality:cost ratio.
Plans for the car
Before you consider any of these options, you should know what wheels you want to run in the exact specs. You should know about your suspension settings before you do this too.
Visuals/ Need vs want
Obviously this comes down to personal preference.
Are you doing this to fit some wider wheels or for a more appealing quarter panel?
Are your feelings short term or long term? Has it been a few months that you've want overfenders or atleast a year?
Maintenance
So front fenders don't matter if they are fiberglass or metal so much since they are bolted on.
Rear fenders are a different story. Because fiberglass and sheet metal are different materials, they will have different rates of expansion. Whether they are molded, or riveted, or mounted using whatever material, they will rub. You will have paint issues. The only way you won't is if the quarter panel is spaced off the body by some small amount, but that would look weird.
So just factor in some fiberglass repair / paint touchup every now and then.
Parts availability
God forbid you get into a fender bender, can you get your hands on the same parts again? I think getting an oem r32 fender will be a little easier than getting whatever bodykit that is made to order with a 9 month lead time.
Project feasibility
I've seen countless dudes selling their 18 x 14 -10 offset wheels for 8k or best offer because they've taken entirely way to long to do the +75mm widebody kit, wide wheels, custom suspension pieces, and bodywork. This will come out to be several thousand dollars. I'm not coming at you financially, but just to state that this is a big project to complete. I know there might be some guys who bought some kit, some "gangster spec" wheels, some 2 inch spacers, and the harbor freight purple paint gun and pancake compressor and are creating zilvia accounts RIGHT NOW to call me a a little I3itch.
Do you really need all that or can you fit some 9 or 10J with reasonable tires and spend time driving the damn thing?
Don't get me wrong, I love seeing kick ass cars. No one is saying your R32 is ass because you lack a widebody kit. Apparently 9J wheels are equivalent to the 6.5J stock wheels in 2023, so don't let my opinion sway you.