stiffer lowering springs accelerate wear on stock struts?

 

Because the shock would have to work harder to control the movement of the higher rate springs.

 

Since you are lowering the strut without providing a shorter strut inner working you are just haveing the strut think that it is constantly at load. (smash in) This will make your strut wear out faster since it is working only at below its correct level of height which the inner workings of the fluids will not lubricate it correctly.