It's much more fun to take the quizzes. The payoff for somebody to take a quiz is to learn something about themselves even if it's meaningless. In comparison, it looks very very difficult to make a quiz with little payoff. Why do I REALLY care about quizzing random people I don't know? I have to come up with clever titles, clever questions, clever answers, etc? I think I'd rather just take another quiz or go do something else.
That said, the main thing I'd do is come up with some interim calls to action between making a full quiz and taking a quiz. Maybe give people the ability to modify existing quizzes. Maybe give people the ability to make a question and give other people the ability to come up with fake answers. Anything at all to give the site some sort of learning curve towards making full quizzes.
I'm guessing you plan to make money from ads, which is why you're trying to get more quizzes (so that it will attract more users to take the quizzes). If that's the case, then you also need to account for advertising to actually inform users of newly created quizzes, etc., before figuring out how much to give away for creating quizzes.
As for other ideas to get users to create quizzes, maybe more prominently asking quiz-takers to create quizzes. Adding in more of a narcissism factor for people who create quizzes (I notice you don't even put the creator's name for popular quizzes on the front page).
Another possiblity: get a hold of Ben Huh at Pet Holdings, Inc (of lolcatz, loldogs, and failblog fame), as they seem to be interested in this sort of thing, as shown by their most recent site, http://graphjam.com.
Also, I think you can still benefit from seeding some more on your own.
Give them an incentive ?
Make it seem like the ability to make a quizz is a privilege awarded only to special users ?
Attach their username to quiz questions that they've added ?
Offer to send them results on how well people scored in their quizzes.
Hope there is anything useful for you in there!
greetings,
Jacques