I think it either needs to be "for each" or "per", not "per each".
well, it's the best card to count curses I've ever seen, that's for sure. But... if you don't want a junker on the board, this is... a colony? I mean both players can buy it, but no-one has a reason to early on, it'll just be a worse Hag. And in the end, it's probably going to stay at 10 VP. Or... 20 VP in 3player. 30VP in 4 player? Do you start playing it, even if you bought it late? Probably depends on the board.
You are right on the wording, I edited the OP.
My thinking is: The player that has (or foresees that he will have) the bad end of the split has more reason to play it, so he probably will. In a slog when to start buying it or playing it is quite a decision. In BM, I don't know, I suppose there is usually a reason to buy it ahead of Duchy, but it can easily end up being worth 0 VP.
I see the scale problem in multiplayer, but also, Curses deplete faster in multiplayer, and there will usually be more than just one player that wants to deplete the pile to stop the one that is ahead on this, so I think it may even be alright. It is possible that the formula for the VP needs adjustment by the number of players, but I have no intuition at the moment. I think the multiplayer dynammics are strange because there is some cooperative thing regarding some players going for it and some ignoring it.
But if you don't want a junker, then the odds are that you also don't mind buying Curses with your extra buys (if you have any), so you can always do that to make your opponent's Graveyards worth less VP. Depending on how heavily he commits to them, a Curse might even be better than a Province.
Sure, there are scenarios in which you probably don't want the card. Most likely, slogs with better Cursers. But it is not that usual to have an engine so powerful that buying extra Curses and trashing them immediately has no opportunity cost. And yes, in those cases, you probably just ignore the card.