All the reward spots will most likely not be claimed but seeing as this is the limit Obsidian chose they have to consider this as a possibility.
That means 6 enemy parties, 50 items, 3 inns/taverns and 200 NPCs will be designed by contributors. In any RPG i've played this would be a huge chunk of the sum total.
I mean, I can see the want to reward high tier backers but i think most people wanted OBSIDIAN to develop this game and not random people/communities off the internet - who will mostly likely have no experience in game design and have no firm grasp of the feel and lore of the game. Maybe im overreacting and the backer input will be minimal but it would be nice to hear more about how those tiers will work.