I think there might be too many levels. Back in the beginning, Level 3 was daunting, and top 50 impossible. And now, as many have pointed out, there's little point to playing anything but Fake Gods, especially as people (zanz perhaps) put the brakes on rare farms. I think new quests, or a campaign type scenario would be cool, but that's pretty involved for a no-pay flash game with ad-support.
Some stats for Top 50 would definitely encourage people to design more ridiculous decks. I think we'd find that fire, poison and vampire decks do a lot better when controlled by the AI then rainbows do...