although it seems wasteful when you could just buy new liners, getting a new boot will mean new toe and heel binding lugs on the boot and new soles aswell as a new liner. depending on how much wear the boots have gotten since you bought them both the binding lugs and soles could be worn and will marginally effect the binding release and by buying new boots these effects are ruled out.
by getting the pro it gives you a pair of boots to take parts off, if say, you break a buckle.
Plus after some reading the 2012 pro has some added features which the 11 kaos doesnt and i think its a 110 flex as opposed to the 100 of the kaos which if you've been in the kaos since 2011 will be a good progression for your skiing abilities.