Yeah that can be real tricky.
Yeap, fortunately the wall is a man-made object and not, let's say, a cliff or anything else that is part of the core terrain and intended to look smooth in terms of material transition. In this particular case I've created several (still working on the exact final number) "copies" of the wall texture, but with alterations. Using the same UVW coordinates I can seamlessly mix these textures across the wall to create variation, as well as additional geometry tweaks to make sure it all looks different.
That's just the outward facing wall for now. The inward facing side of the wall will be more traditional in terms of material detail, since making several textures for each section of the level would take too long.
The good news is, I suppose Siege is nearly an "urban/industrial" map in some ways, due to the amount of man-made terrain as cover. And that was a very popular request for APB maps.