I know you came up with this a while back, but having read through it again a few weeks later I still support this wholeheartedly. I know for many slayer is their favorite thing to do but for others, who prefer skilling, it really isn't interesting. So on top of improving slayer for those people who really like it I think that fleshing it out in the ways you've mentioned (such as making the mould easier to get/those boxes) would entice those players who don't care for the skill much.