A good thread which will no doubt get a lot of views and hopefully many contributions.
I'm another who started messing around with the Airfix MGB as seen in the picture below.
The red painted car one day will be finished as the 1966 Marathon de la Route car, the middle one is abandoned as it was to be an MGC GTS, but now I have the GTM version, and the left hand one was also to be made into a 'Sebring' style car, albeit in modern form as an MGBGTV8 racer, thus the ST spoiler. Now another GTM model will be used.
Another picture of the Marathon car.
The hardtop is built with styrene sheet.
I did actually look closely at the kits, and without a doubt the earliest ones I bought, in the original white plastic are the best. The newer the kit, the worse the moulding seems, especially round the sill area.
Regarding the grille, John at Classic Slot (Ocar) used to be happy to supply parts separately, and I bought a couple of photo-etches grilles from him. A great improvement over the Airfix one, which even on my early models are awful.