I've been meaning to respond to that, DStu, but I haven't had a chance to.
I think the Potion cards play very differently when you have more than one.
As you say,
Once you have them clumping together, you can almost auto-buy the Potion.
And it's true - the question of "Do I want a potion or not" often becomes trivial, with the answer being yes, you want a potion, far more often.
But it gets replaced with other strategic questions. First off, buying TWO potions suddenly becomes a viable option, if you want to get the potion-cost cards faster. It also makes mid-game buys have more thought to them. If you have 3p, 4p, or 5p, and there's only one Potion-cost card around, you're probably buying that Alchemist, because you have only one potion and you're building an alchemist stack.
Whereas, if there's, say, Vineyard, Alchemist, and Golem, suddenly there's different options. Late-game switch to vineyards, mid-game get either alchemists or golems perhaps depending on what other actions you've managed to pick up. It's less likely to be a rush for a single card, too; if there's both alchemist and Scrying Pool, either one can do for card draw, though depending on the board one might be slightly better than the other.
So yeah, I think if you have more potion-cost cards, you're more likely to auto-buy the potion. But there's other strategic considerations that crop up that wouldn't happen in a single-potion-card setup.
It's a different sort of game, but I don't think it's better or worse, just different. Both seem reasonably fun (I try to play a mix of both
)