It doesn't dent... it breaks.
Used to be significantly lighter, and on an 84 it may still be, but with the thin crap that cars are made of now, I'd be willing to bet that it's pretty close... and glass may even be a bit heavier.
An accident is a concern. The front fenders are your primary crumple zone. The frame is a secondary.
With glass fenders, they are going to shatter, and make your frame your primary crumple zone... a relatively minor accident would mean a bent frame.
Personally, on a DD, I draw the line at a glass hood (and prefer steel).
Now, on a late 60s muscle car, ya... pretty much no crumple zones there, and the stock steel is heavy.