The only caveat is that AES is not necessarily a black box. It's possible there may be hidden structure to take advantage of, but if there is there's no reason

The only caveat is that AES is not necessarily a black box. It's possible there may be hidden structure to take advantage of, but if there is there's no reason to suspect it's one that's amenable to a quantum speedup. As far as the Grover speedup goes, it's already optimal. Requiring O(sqrt(N)) queries is the proven lower bound for unstructured search.