Now, i'll preface this by saying:
Yes, i know the Tiamat is designed without optimization in mind. I mean, it's whole purpose is 'big ship = big fun' (which definitely holds true). But, you certainly weren't lying when you said it would toast medium-low end systems. Also, i have absolutely NO experience with modelling / programming so take my suggestions with a grain of salt.

Idea: Swap the large grates along the sides and bridge lights behind them with flat textures. That's a lot of polygon faces all for a single (really well done) effect. Now, i noticed that because it was specifically bridge lights behind the grate it would have the effect of EVERYTHING turning orange once the CICs were destroyed, and i have no idea how you could replicate that in a flat texture.

Oh, and i realize that Marduk has either released or is close TO releasing, so i hope i don't come off as an ungrateful person using entirely free stuff and complaining about it.