You could try this: duplicate the model, edit using Symmetry, then copy the Unwrap modifier from the original object's stack to the new object. Dunno if it'll work but it might be worth a try.
Question: are those merged into the same object or are they separate objects? I'm frankly amazed if you got that many polygons into a single batch without hitting big problems.
One main problem you are facing is that you created everything as ONE object. Try to seperate the scene into smaller objects. So you are able to reuse parts of it.
thanks, Looks promising; how can i use "paint effects" on an objects faces (with each placed object perpendicular to the face) rather than just a plane?
Instead of rotating object you could rotate gizmo. For example in 3ds max when cylindrical projection selected you manipulate gizmo like a usual object: