Wait, Lorry I didn't understand half that. WHY would we need a rule prohibiting whatever it is your saying from attacking battleships or whatever? I don't even get what your saying in italicize.
Battleships are stronger than any other ships, but their 1500 cost will make them rare. Thus meaning there is no reason to make rules prohibiting it from attacking others (I'm gathering this from what you said, but again I think I misunderstood it).
The BS is supposed to be the god of gods in ships. The cruisers are supposed to be the less-expensive ones used for attacks, where the BS is primarily defense and sieges.
And your wrong about people not buying it. AW would have at least three. Mine, and the flagship, then Korrd's, and then Alpha's. I imagine the SF would also have 2-3. And I know Kreig's BS isn't going away.
Heck, nowadays I see more Corsair Dreadnaughts than any other capship outside of Cambridge (in there I see many Bret caps.. SF spams them..). This is because its a battleship, and because the targeting is so screwed up that people can't target it, making it extremely unbalanced. Increasing the cost would make these more specialized. Taking people a LONG time to get just one. Also, would make factions gain them faster, making them more powerful than normal solo-freelancers, AS THEY SHOULD BE.