I would say no to fibreglass....
1) It would cheapen the look of your car.
2) Replica kits always do not fit properly and some work would be needed to fit it properly. ( involves modification and thus extra labour costs)
3) If u r gonna get 18" ACS or have them now, it means u gonna lower ur car, and with the kit close to the ground it can very easily crack. I've seen so many cracked bumpers (all fibreglass) on cars and they are not easy to fix. Speed bumps and raised driveways will be feared as extra caution going up and down them.