Acyually, we do have a missile boat, if a poor one: the Buffalo mk2.
This COULD possibly give the Buffalo some actual value (rather than just an easy to kill target and resale hull.) But yeah, given the missile weapon selection in the game and the spread of Missile mounts across vessels, there's not much of an ideal missile boat in the game (yet) to take full advantage of this. If we had more variety on the large missile launchers (other than the MIRV and Reapers), then the Astral, Conquest, Apogee, and Aurora could make for decent support fire vessels with a NARC-type support weapon. Otherwise, the best "missile boats" in the game are things like the Onslaught (4x Md Mssl), Dominator, and Oddessy (3x Md Mssl each). The Oddessy I can see in a support-fire role, but doing so for the Onslaught and/or Dominator would be a waste in those cases.