Well you need more resolution there. You can run edit Polys>Subdivide on just that region, but remember... the more resolution you add, the slower your renders will be. What you need to ask yourself is how close are you really going to get to the word Lego in your project. In all likelihood, you could get away with using a bump map and not a displacement. It will render much much faster and be smoother, but on super close ups it won't look quite as good.