I wonder if any of the photographers who extoll expensive lenses for 6 to 10MPX APS-C dSLR's realize compared to individual grain size in ISO 100 film a digital sensor site that records one pixel of information is huge. So then how can small differences in lens sharpness make so much difference?
I doubt very many have made a simple test to realize where digital sharpness comes from? All dSLR's have menu controls for recording quality that usually allow reducing to zero or almost and increasing sharpening by the camera's firmware chip processing. Every dSLR user should make a test to understand how digital sensors record subject information - just set recording to Raw at full image size, put the camera on a tripod and focus on a detailed sunlit scene, and expose one shot at the normal (mid) sharpness setting, and then on your menu for picture recording quality turn sharpening down to the lowest setting and shoot the same shot again.
Download the two files to your computer and open them in Photoshop without adding any sharpening in Camera Raw conversion. Then zoom into the same small section of image detail on both test exposure frames to 300X or greater so you just begin to see the individual pixels on-screen.
The differences between the sharpened and unsharpened Raw captures should be considerable, with the unsharpened frame very, very soft compared to the sharpened frame.
I think you will conclude that dSLR sharpness is achieved very little by any difference in lens resolution compared to the camera's built in processing chip sharpening.
That does not mean lens quality is not important. With wide angles curvilinear correction to eliminate pin-cushion and barrel distortion and render straight lines actually straight is very significant. And in long lenses correction of chromatic aberrations so all colors focus the same is also critical. And probably the most significant factor with zoom lenses is because they have many, many different glass elements internal flare and diffraction can reduce recorded image contrast between subtle subject details.
But, all the criticism I read of "kit" lenses I think is less about real image recording and more about buying expensive bragging rights.