A hot cam and bigger carb will cost you low end power and torque. A 12:1 piston will require premium gas or better. If you get any increased power, it will be at higher RPMs. The increased power (if any) and higher RPMs will strain an already tired and worn bottom end. You will be taking the motor apart to replace the old bottom end soon. That is, if it doesn't simply let go on it's own and your connecting rod fly throught the bottom of the crankcase.

Said another way, the tired top end is actually protecting the tired bottom end. Bring the top end up past 100% without an equal strengthening of the bottom end results in early bottom end failure, every time.