I might just be crazy and looking at it wrong, but with slayer, it seems like the only thing it's good for is starter/rebuild money. It really starts to fall behind on pkp per hour compared to most, if not all, bosses.
One little fix that wouldn't jack up the pkp per hour too much, but add a little excitement to the skill and give some people more motivation to do it would be to maybe give slayer keys something like:
1/1k chance for reg slayer helm.
1/2k for a slayer helm (i)
1/3k for the Wildy weapons.
1/5k for a new slayer key specific (untradeable) pet, maybe the bloodhound or something.