As a modeler who uses the "smoothing group turbosmooth turbosmooth" style. This modifier would be immensely helpful and would cut down on a lot of wasted polygons.
The polygons are streching becouse they aren't capped/connected into triangles or quads. You should do it this way. :) Don't forget to have Angle Snap Toggle ON
So this is not a polygon plane placed in front of the wall? It's a layered shader? layered texture? or what? Here's one common way: http://wiki.polycount.com/Decal