When Enzo was alive, all Ferraris built for racing had the shields and all Ferraris built for the street did not have the shields. There may have been exceptions, but his intent should be clear. You may as well badge your car as a 430 or an Enzo or something else it is not. Just my opinion.
I think If it's not OEM it can make a car look cheap. It's rare that aftermarket parts can match the look or fit and finish of factory parts. I think shields need that recess to really look finished.
Factory installed shields (not removable,with fender indentations) are great. I would not however,put neither sticker nor metal aftermarket shields on the car that did not have them originally.
I'm a huge fan of the shields, as I'm a huge fan of the racing team. If a car wasn't campaigned by the factory, Scuderia Ferrari or SEFAC or Ferrari S.p.A., it shouldn't have shields on its fenders, ever. It's really quite simple.