Good thoughts. Incidentally I didn't mean to be mysterious, I just didn't have time to complete my post this morning! Basically, I postulate that the first wave of Starship (AKA Constitution) Class ships had much thinner saucers., about one deck thick. However, as they achieved higher and higher speeds the outer half of the saucers began to fracture. The overall shape was still fine for optimal warp geometry, it just needed to be stronger - so an array of structural integrity boosters was installed around the rim. These were in turn covered up by standard hull plating, which was blended into the existing shape of the hull. The atmospheric aerodynamics of a separated saucer were just a bonus! Future builds of this class simply retained what worked.