I don't like the ideas so that much, to be honest.
Cursers are already strong cards and if there aren't strong trashers available, it's even more decisive whether you win the curse split or not if they destroy more of your points. Further, if they are randomly mixed to the curse pile, you can end of with 5 to 5 curses, but -10 to -5 points, which is ahuge gap.
That's about the idea in general, now let's look at the cards.
Slough is quite weak, even if you have 6 Super-Curses in your deck, you need 2 of them just to be at the start again. And again, it's a bit unfair if youre in a curse war and you get the super curses (great for Slough) and your opponent has the -1 Curses.
Curse Upgrader is weak, Silver is better if you haven't 3 Curses or more in hand and you have to connect the cards.
Curse Cleaner is very unbalanced, you even benefit the player if he manage to trash a lot of bad cards, if he has just 1 to trash, it's weak.
Curse Propector is a cheap, embargoed village in non-cursing game and a no-buy in cursing games (if theres trashing of course), so again, very weak.
And don't forget that all the cards are almost pointless in games without cursers...