What about resale value. Do collectors want fiberglass? Since the bodies cost about the same who will get more at sale time?
No, they don't.
For Bronco people who know what is going on, a fiberglass tub on a street rig means that the body rotted out. And the frame probably has a bunch of hidden rot about to come. Doesn't matter if that is true or not, that is just what is expected.
A decent collector will be turned off by bedliner as well. It is a well know way to hide rust. And any collector car/truck the biggest issue is dealing with rust. A clean steel body will be the most desired.
For a race rig, a glass body isn't that big of a deal. Body panels are consumable. You can get light weight bodies. At which point you are really just buying the race parts in a collection and by chance it happens to be bodied (and maybe an original chassis) of a Bronco. So not really a collector.