I use naval design on some of my ships.
The reason is not puely esthetical - the battel efficency of good designed ships is terrifying.
I use a battleship-like designes mostly, since a ship that has it's heaviest weapon in such turrets, can focus most of it's firepower at any point in space.
As for the nomenclature...One can expand on the existing one to fit in with the new ships.
D - destroyer
HD - Heavy Destroyer......that's no biggie
One can allso put in completely new classes and name then however one likes (as long as the clases are plausable)
It's totaly stupid to invent a new class for ship that not different from a standard destroyer.
If you have something new - like a Missile Cruiser/Corvette (allmost completely armed with missiles), Carrier or a Battleship, why not name them with a new calss designation?
A carrier and battleship will fit in neither the cruiser, frigate or destroyer designation., so you must invent a new class anyway.