Never thought about the extra stiffness and it could change the tie up of the panels.
I have done other kayaks where I did not glass the inside and they can crack when you land on rocks etc.
To restate the problem:
I find it hard to glass the inside and keep the resin to a minimum without "floating the glass", and I always seem to be chasing out bubbles as the glass wants to slide down the inside. Minor bubbles but I always think that there is more resin than needs to be and you can't squeege it off like you can on the outside.

Thanks for the responses,

Paul