That's an interesting situation. Are the cracks on the cockpit sole or on the seat-fronts (or even on the aft-vertical section)? Maybe a pic or two?
Strengthening involves laying-up additional layers of 'glass from the inside. It won't necessarily reduce gelcoat-cracking flex. Stiffening, on the other hand, is a whole 'nother ball of wax. Google-up "hat shaped stiffener" to learn about them. It's not hard, but there's an involved principle behind it.
I would be more concerned about your gudgeon-area cracks (rudder pivot). They could indicate a rotted-out plywood backer on the inside of the transom. How does that area feel from the inside if you poke at it with an awl? Mine was entirely pulp, and indicated a complete replacement. It was a big job, but not terribly time-consuming. I wrote it up here last year sometime.
