If curation rewards are removed, surely large holders still have content visibility control as an incentive. Maybe this isn't such a bad thing and can be considered more of a balancing act. As dan said, the curation system may be fundamentally broken when large holders can game the system not for the benefit of the system but for private gain.

As for answers to your question, I think the incentive to buy steem still remains, except just one fractional aspect of the incentive would be gone. People will still buy it for the ability to make steem denominated interest at a rate higher than else where, they will also retain the content visibility voting power, whether or not this is important to them i don't know. And of course, the speculators will continue to speculate.