Yeah, usually with large objects, you will try to create it will tileable textures and maybe use vertex paint and shader to make it unique. For an example, take a look at this tutorial: http://eat3d.com/free/vertex_painting You can do a LOT with shaders, and use the texture channels.
your over-thinking it, also modular dosnt mean you need to import hundreds of pieces into udk, you can build it as one mesh in max or maya, and just have lots of different pieaces share the same UV space, and for large areas doing a lot of mapping to tileable textures and trim sheets. can bake AO to the vertex colour also…