Excellent tutorial. If I may add a little something, a good way to get rid of tiling is to use a decal layer. You can use a different mapping channel so you could for example do graffitti, dirt, shadows, posters etc on a separate texture with an alpha channel and then map it on top of the excellent example above
Instant grime and less obvious tiling. Not that the tiling is obvious in this case, just thought I'd add it. I hope I'm not stepping on any toes.