There are a couple of challenges that I think the Steemit platform will face as more users come aboard. One is what you've described - essentially that the system has built in incentives to repost and no way of penalizing that sort of behavoir. Another is the large amount of spam content, again without any mechanism to control or penalize it. These things will need to be addressed by the devs or we will end up with a network that contains more noise than signal. But we are still in Beta and I have confidence that improvements will be made.