Actually the critical factor was the effect of the Confederate cruisers on insurance rates, causing northern owners to reflag their ships to largely British registration. British financiers, politicians and insurance firms must have cheered. The underlying question was how vulnerable was the north to drops in shipping to foreign ports? What materials were so critical that they could not have been replaced from the resources and manpower of the north? Even if a blockade of sorts to New York, Philadelphia, Baltimore and Boston had been possible due to the presence off-shore of southern raiders it would not have reduced their ability to wage war on the south. Critical shipments of men and equipment would have continued under the protection of the Union Navy. A very different situation faced the south. Although they traded large amounts of cotton across the lines, their lack of manufacturing required shipments from Europe of military goods, medicines and even bulk clothing. One interesting question is whether there existed domestic shipping insurance in the south during the war? I can't imagine a worst risk than a runner. So for the south the name of the game was either cash or cotton for purchases, although the cotton bonds were a cute idea.To me, far more than the wasted resources involved with the ironclads, Mallory's real mistake was his infatuation with commerce raiders.
Sure a good captain could take, say, the Alabama on a long Atlantic cruise and sink or capture a bunch of US shipping. But so what?
The north had thousands of civilian merchantmen plying the high seas and it would have taken dozens of Alabamas a couple years to put much of a dent in trade.
And when the lists of captured or sunk ships includes whaling vessels and other such completely pointless "victories", someone should have asked why.
As noted, there was never any kind of organized naval strategy and no clear cut goals, which is always a killer when it comes to fighting a war.