I have never had a sprue plate break... and I used to whack them open with a wood hammer handle. Nowdays I just push them open with my gloved hand.
Everyone else has covered the other stuff. Make sure the faces of the blocks are clean, no "spatter" on them. Make sure venting grooves are clean. Make sure edges of cavity aren't "burred". Take your time when closing the mold to make sure the halves mate together properly.
I've always had good results with my Lee molds. Really no more problems than I've had with my iron ones.
I always felt that if I got to the point where I thought it was time to bury my firearms, it was actually time to pick them up..