Slumber is pretty neat. Would be nice to see it scale off GSF enchant/necromancy like normal sleep does, and have Dream Eater interact with it as well to help one of the worst sorcerer kits out.
Yeah, having that +2 spell DC increase at level 8 would be nice to see on Slumber too. It's a big thing to take it over plenty of useful level three spells. Or switch the DC increase from Sleep to Slumber instead. Would give further reason to grab the spell.
But I dunno DE being such a poor perk altogether. It's a bit limited but has its moments.