Looking good so far.
I don't know what everyone else does to make stuff look ruined, but here's what I do.
(I put the images in as URLs so that I don't clog up your thread)http://img51.imageshack.us/img51/6505/example1p.jpg
Go in the 2D shape editor and make a shape like the one in the link above. Then do Extrude to Point (and make sure the point thingy is in the center of the shape).
Once you've done that, line up your 2d shape with a wall or a column, like so:http://img594.imageshack.us/img594/6209/example2ni.jpg
Then subtract, and viola! You got a crack in the wall. The example shape I made doesn't look very good, though, so try to make your shapes not so square like; make them kind of uneven. I think
this is the method that Epic themselves used when making scars and cracks in maps like Velora or Ruins. I've been using it for a while, and sometimes it turns out okay, other times not so much, but it's probably because I'm terrible at making 2D shapes.
Edit: You might actually want to put the point at the bottom of the shape. I'll have to experiment a bit to see what I get.
Edit 2: I just noticed I'm a Skaarj Assassin.