If the floor pans are bonded I would expect a tiny increase in stiffness but it wouldn't be much. If they are just bolted and sealed it will be insignificant. Call me a Luddite but I do like the idea of sitting on wood.
Way back, a chap with an MGB ran over a piece of scrap metal in the dark. It came through the passenger floor like a can opener, and was stopped by the cross member. Makes you think.
Trad Morgan seats in more recent cars do have a deflector plate at the front.
