Hmm.. yes this seems to be a bad idea.. A better way: use tiling for the normal color skins, and and make seperate clones of the building model for the baked on texture, then make them almost the same size as the normal buildings, and just blend over the old buildings with the new building.. see what i am saying? This save your from having to make tons of huge textures, and if you want baked lightmaps for instance, they can be much lower resolution...