Yes, that should work, decals are quite effective, as also are detail textures, slightly displacement alpha changes, detail sprites, even normal maps. There are a lot of techniques to reduce tiling. Using good quality and high resolution textures for ground terrain is also basic to prevent tiling. Regarding memory requirements, all those texture techniques scale well on this engine, is not a big problem. My concern is about displacement resolution needed to make terrain not very bland, and then brush work, and of course: lightmap scale needed. Lightmaps would need more texels to look like 1:1 maps.