Stalingrad wasn't the target...
Stalingrad wasn't the target of the 1942 offensives (the Caucuses were), and only became a target after things had already begun.
In many ways, however, Moscow was not nearly as important by 1942, as most of the critical industry had been moved from that region (optics in particular, though lots of electrical manufacture as well), and some alternative rail lines were under construction. It's seizure by the Germans would have been a morale blow, and certainly not to be hoped for, but ultimately it wouldn't have made an enormous difference by 1942.
More to the point, it was also too close and too limited a goal for the Germans in 1942. They still thought that they had a chance to knock the Russians out of the war, and the ambitious (i.e. insanely overreaching) nature of their plans for Case Blue bore this out. Moscow was more along the lines of a 'small solution', and wouldn't have contributed to an overall Russian collapse, which is what the Germans were aiming at.