Quote: "With entities, you can't just retexture to change where say, a drain pipe was to be honest."
Why not?
The only real difference between entities and segments is the way the engine looks at them (this includes better collision detection for segments). Both choices still
look the same in-game. If you plan on making the building accessable to the player, use segment walls to build the layout/foundation of the building and then accent them with entities such as pipes, windows, balconies, and so on. If the buildings are far away from the player and inaccessable, a simple 6-polygon plane with a texture slapped on it's side will suffice. No reason to add an extra 200 polygons via segment walls when 6 polys do the job just as well.
If buildings are close to player but still inaccessable, entity planes decorated with aformentioned entity accents (windows, pipes, etc) will again save you several hundred polygons as opposed to stacking wall segments (unless you're familiar enough with the segment building process to optimize your segment meshes as well as Wizard of id has done). Extra detail in your texture work, and a clever combination of segments and entities in this case, should get the job done convincingly. So my advice would be; don't restrict yourself to using only one option over the other. Use both as they're needed.
Kravenwolf
