Instead of voting on submissions, why not have a weekly AI challenge whereby people making submissions would also submit code for the challenge? As the week progresses, you can improve your code, even for submissions already made.
The ranking of the front page of submissions would be based on the ranking of the associated programs for the AI challenge. Points gained by your AI program would be divided by the number of submissions associated with that program.
The AI challenge setup would be similar to the Google one: http://ai-contest.com/
What do you think?