I find port and starboard markers at the end of hallways and at the mid ships point help to keep a sense of direction and adds points of interest to break up passage ways and add some depth. I also like having a point in the vertical levels of a ship that is 'below decks.' I've done this on the Yamato, at a certain level the hull changes from blue to red, I've kept the colours showing internally in places like the elevators so you know when you've gone 'below.'
Changing lighting and dominant colours also helps, ie I have a docking area where I use a lot of hazard, have yellow lighting and decorations, yellow deck is docks. Similarly I keep the birth deck lighting dim and cool and have the mess hall lighting bright and well lit. Lighting is the easiest way to give a subtle sense of a change of place. Doesn't have to be over the top, just little highlights here and there, if the highlights are predominantly a certain colour on certain decks or locations it helps to define the place without breaking your overall theme.
Detailing a big ship is a lot of work and takes time and multiple passes on the detailing.With your passages I think you should break up your floors and ceiling some. You have a good theme in the walls but the floors/ceilings are all one block which is visually overwhelming. Floors and ceilings in ships always have hatches and panels, rivets, lumps, bumps, carpets, mats, vents, grates, piping, girders, scaffolding, etc. Take a look on google images at internal pictures of ships, commercial and military, lots of ideas there.
Big job for sure, but you're already breaking it up a bit with side projects which is the way to go. Keep at it.
