I'm pretty sure the locking up thing is more due to the way a drum brake works than anything else. When you stomp on the brakes the shoes are flung outward and the way drum brakes work is that the shoes bind up inside the drum. It works kind of like a moving wedge between the pin that holds the shoe and the drum. Not much actual pressure is applied by the wheel cylinder.
An adjustable proportioning valve didn't solve my lockup problems. I don't run one anymore because I didn't need it. Plus, I sold it to a kid for more than I paid for it.
I don't know about pads wearing faster than shoes either. Maybe they do, maybe they don't. I know shoes don't last very long with mud in them which is why I used to hose out my drums every Sunday. I know my shoes didn't last as long as my pads in the front, we'll see if my pads in the rear last longer than the ones in the front.
