reviews are very important. There lots of customers that wont buy a product unless it has some number of possitive reviews. In fact, it helps the developer to focus on which products to do, or what kind of products the customers want. I wont say nothing about the realtionship with tiers cos i dont agree with that, since creators can review their own products and earn tier points about that ( yes, tier system sucks).
Another thing, there lots of ppl that dont even know what a review is. Giving more focus on this would be very important for both developers and customers.