Wow, never expected Cloister would provoke such a discussion! My expectation would be that, as originally posted, it players would ideally go for it early in order to fuel some early VP without clogging the deck (whenever possible, when cloister is in hand, buy cloister). Clearly in late game when clogging is going to happen anyway, the difference is negligible. Would it be better to make it cost $4 and give 2VP tokens on-buy instead?
I prefer to keep the VP gain on-buy rather than on-trash. I like the idea of it being a hovel for you once you've bought it and got your VP. Makes an interesting passing card for Masquerade. And I'm not much concerned about it having two lines. It's minimal text and simple conceptually.
An alternate version of Labyrinth:
In trying to make a similar VP token gain effect but avoid the infinite spamability of, say, a tiny deck full of Labyrinths and Warehouses, I came up with this. The VP is still potentially limitless, but the speed you can gain it is not enough to allow you to beat your opponent without going for traditional VP.
It's a Reserve-Reaction. (Yeah, I know there's no official card like this.) It reacts to reshuffles. It never clogs your deck (except, say, gaining it through Armory). But you can only call it for points one at a time, and only at the start of your turn. Not sure whether I nerfed it too much or not quite enough.
Rule clarification: Only Labyrinths that are actually in your deck when you shuffle it are subject to Labyrinth's ability. If you have any Labyrinths in your hand or play area when you shuffle your deck, they stay where they are.