Something that would also help: put guardrails on the sides of the platforms and stairs. Its a service tunnel and we wouldn't want workes falling off would we?
That electric box you had worked well, so I'd say try to find more similar industrial type entities that you can place in different places. Maybe some metal support beams on the walls too. Service tunnels and those sort of places are usually smaller and narrow so it might be a good idea to make the rooms smaller. Not only will it be more realistic, but you can then also put a lot more entities and decorate the rooms better.
Hope it helps
H.K.
http://fpscx10.mygoo.org/index.htm?sid=b9908f90a6ff35bbc42ee87032e4f3e0