Back in the day, if you said the RPG could be used as a reasonably cost-effective anticraft weapon, you'd be laughed at. After the Somalis figured out the idea of welding an angled tube on the back of the RPG, no one is laughing very much these days. (Tis how our Blackhawks were shot down.) RPG's produce backblast, aiming one up high enough would fry your legs. Until the Somalis used a couple cents of steel tubing to redirect the backblast. Volley fired, they can and do shoot down some of our helo's. The insurgents in Iraq seem to have picked up on this trick also, with varying degrees of success.
At first glance, these underwater missiles don't seem very practical. However, never discount human ingenuity. I have few doubts that the Iranians could figure out a way of making them very effective under certain circumstances. I could come up with a bunch of ways of using them, and I have zero Naval experience. Why not put some at the bottom of the ocean/Gulf/whatever, aiming straight up? Hide them in sunken wreckage, and a mine sweeper is unlikely to pick anything up. Volley firing is another tried and true method.
Another possibility is that they do not intend to be fielded whatever. Announce very publically they're making 'supersecret' modifications to these missiles for coast defense (or whatever). We can't ignore it, because it's more than likely to be true. And it potentionally makes a pre-emptive invasion look even less inviting to our brass. Never underestimate the psychological aspect of weapons, or even war in general.
First strike usage of nuclear weapons in a non-nuclear war is not US policy, and probably never will be. From the Korean War on to present day, more than a few folks have said "If we just nuked 'em, the war would be over by Christmas." It's never happened, and likely never will. Possible, sure. But about as likely as me single handedly winning the next Superbowl. Every time we occupy a foreign country, it turns into an infantry war. Fancy toys like super neato fighters, super high tech missiles, super nifty ships, etc are very nice toys. Yes, they can be helpful, very helpful at times. But they cannot win a war. Unfortunately, that will likely always be reserved for boots on the ground.