while dressy shorts and a collared shirt are acceptable, why not consider the khakis and button down shirt?
they aren't really that much more uncomfortable, and you show a little more respect for the surroundings. the CG is indeed the flagship restaurant of wdw and the surroundings certainly convey that. i have seen many folks there in shorts (and what you consider dressy and what others consider dressy may vary widely) and shirts that i would not call business casual.
if the surrounds bespeak elegance and class, don't we owe it to the establishment, and to the others around us, to acknowledge the effort they have put into presenting us with an elegant meal by dressing accordingly?
they certainly treat us at CG like upscale, elegant consumers, i think we owe them the same respect by treating OURSELVES that way.
just my humble opinion