It actually makes sense that you get a bit more plank wear, if you stiffen springs and the car grounds a fair bit.
With soft springs, the car "rebounds" a bit when the plank connects to the tarmac. Think of it as dropping a plank from you hands. It also jumps up when it hits the floor, albeit not that much.
Stiff springs resists this "rebound" effect and forces the plank back on the tarmac. Stiffer springs will only save plank wear when the plank just has glancing blows on the tarmac, not when it solidly drags along.
It's only after we've lost everything, that we are free to do anything.