With a v-brake, the barrel adjuster only changes the distance the lever/pads travel before engaging the rim. Mechanical advantage will remain constant regardless (hence the term 'linear pull' brakes).
If you do want to try changing the mechanical advantage for weaker/stronger brakes, look into 'Avid Speed Dial' brake levers. These levers have adjustible cable pull.
Inability to easily alter mechanical advantage to personal taste is one of the reasons all my bikes use traditional cantilevers instead of v-brakes, disks, etc....