If you're like me, no matter how well the system performs, you'll never be totally happy with it if the case is significantly damaged or defective. You probably won't be ecstatic with your finished product if the case doesn't look good even if you know the internals are perfect.
Then again I know a couple guys who just stack their components on racks that're ugly as sin and seem satisfied, so maybe you don't have the same compulsion I do.