Figureheads:
Skull
Giant spike
Dragon (not just the head)
Unicorn
Gargoyle
Mermaid
Christmas wreath
Decals:
Flaming skull
Flame decal
Bomb
Jolly Roger
Themes:
Goth - Like royal except the railings and lights are black, the banners are either black or red, and maybe a few spikes or gargoyles here and there
Frozen - Frost around ship, torn banners or flags hanging from ship, frosty crates and winter gear lying around ship, hanging lanterns for lights, maybe a snowman somewhere
Pirate - Stacks of cannonballs, treasure chests full of booty, guns, swords, and barrels lying around, bottles of rum or beer lying around, maybe a pirate flag on the back
Bandit/Raider - Spikes, weapons of all sorts lying around, makeshift armor in some areas, maybe some bullet holes
Christmas - Garlands and wreaths hanging from railings, ledges, and other areas, christmas tree or two, candles, candle rings, and nutcrackers lying around
Halloween - Spiderwebs all over, jack o lanterns and skulls lying around, cauldron or two
Ghost ship - Torn flags and banners, whole ship is grayish black and looks very battered, once again maybe some bullet holes
Nautical - Crates, oars, harpoons, life rings, and maybe an anchor or two lying around, hanging buoys (the old glass ones), barometer on a wall, lanterns for lights
I also like the "homey" theme suggested earlier, I would really like to see that
Dyes:
Ability to paint metal and wooden parts
Purple color
Pink color
Rainbow
Make dyes reusable