I also think that it would be more simple if the card effect was decided on when you gain it. In fact, what if you could alter the effect every time you gain one, changing the card mid-game? Here's an idea:
Cloister, 4$, Action
+1 Action
If your Cloister token is face up, trash up to two cards from your hand. Otherwise, +1 Card, +1 Action
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When you gain this, either put your Cloister token face up or down (it starts face up).
My only issue with this is that something like this will usually behave a bit similar to a Seasons card (see my thread linked in my signature), because people will change it depending on game phase. On the other hand, it doesn't need a Season mat and has player-relative timing. That's really cool.
My reason to argue for the ability to change the card mid-game is mostly based on the assumption that it'll be hard to make effects that are so similar in power that different players will pick different abilities. And if they don't pick different abilities, it loses a big part of what makes it interesting. Of course you can't enforce different picks, either, as that'd be unfair. Maybe it's not as bad and people will pick different options often enough... You could help this by making the effects interact with each other, of course, e.g. by making one a trasher and one a Curser and similar things:
Rebel, 5$, Action - Attack - Looter
+3 Cards
If your Rebel token is face up: Each other player gains a Ruins.
Otherwise: Trash up to 3 cards from your hand.
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At the start of the game, put your Rebel Token on any side.