Why was this utility important to the U.S. Supreme Court, in your opinion? What were they going after? Why did they ask the question?
The Miller case was interesting because Miller fled before the appeal was heard, and did not appear to prosecute the case. The Supreme Court, I do not believe, received any argument from Miller's side and disposed of the case on the narrowest possible grounds.
For jurists who accept the theory that only arms suitable for militia use were envisioned by Madison when he wrote the amendment, as the majority opinion written by Justice McReynolds indicates the Hughes court did, it naturally follows that they would also believe that possession of a gun that has no utility as a militia arm is subject to regulation by Congress. But I think that theory is inconsistent with the intent of Madison's proposed amendment which was approved by Congress and and ratified by the states. In addition to the comments by Madison himself concerning the people's right to possess private arms, ten days after Madison introduced the 2nd Amendment in Congress Tenche Coxe wrote and published; "As civil rulers, not having their duty to the people duly before them, may attempt to tyrannize, . . . the people are confirmed . . . in their right to keep and bear their private arms."
Coxe's comment was given Madison's blessing and was widely reprinted without contradiction by him. That should be enough to give a good indication of Madison's intent for his amendment concerning the possession of private arms of all kinds, and not just those with "utility" as militia armament. Since Madison made no secret of the amendment's intent it must have been known to the members of Congress who ratified the amendment, which indicates their intent as well.